HiEventsDev · daveearley · Jan 30, 2026
diff --git a/backend/app/DomainObjects/AccountConfigurationDomainObject.php b/backend/app/DomainObjects/AccountConfigurationDomainObject.php
@@ -13,4 +13,9 @@ public function getPercentageApplicationFee(): float
     {
         return $this->getApplicationFees()['percentage'] ?? config('app.default_application_fee_percentage');
     }
+
+    public function getApplicationFeeCurrency(): string
+    {
+        return $this->getApplicationFees()['currency'] ?? 'USD';
+    }
 }
diff --git a/backend/app/Http/Actions/Admin/Configurations/CreateConfigurationAction.php b/backend/app/Http/Actions/Admin/Configurations/CreateConfigurationAction.php
@@ -28,6 +28,7 @@ public function __invoke(Request $request): JsonResponse
             'application_fees' => 'required|array',
             'application_fees.fixed' => 'required|numeric|min:0',
             'application_fees.percentage' => 'required|numeric|min:0|max:100',
+            'application_fees.currency' => 'sometimes|string|size:3|alpha|uppercase',
             'bypass_application_fees' => 'sometimes|boolean',
         ]);
 

diff --git a/backend/app/Http/Actions/Admin/Configurations/UpdateConfigurationAction.php b/backend/app/Http/Actions/Admin/Configurations/UpdateConfigurationAction.php
@@ -27,6 +27,7 @@ public function __invoke(Request $request, int $configurationId): JsonResponse
             'application_fees' => 'required|array',
             'application_fees.fixed' => 'required|numeric|min:0',
             'application_fees.percentage' => 'required|numeric|min:0|max:100',
+            'application_fees.currency' => 'sometimes|string|size:3|alpha|uppercase',
             'bypass_application_fees' => 'sometimes|boolean',
         ]);
 

diff --git a/backend/app/Http/Actions/EventSettings/GetPlatformFeePreviewAction.php b/backend/app/Http/Actions/EventSettings/GetPlatformFeePreviewAction.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace HiEvents\Http\Actions\EventSettings;
+
+use HiEvents\DomainObjects\EventDomainObject;
+use HiEvents\Http\Actions\BaseAction;
+use HiEvents\Resources\Event\PlatformFeePreviewResource;
+use HiEvents\Services\Application\Handlers\EventSettings\DTO\GetPlatformFeePreviewDTO;
+use HiEvents\Services\Application\Handlers\EventSettings\GetPlatformFeePreviewHandler;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+class GetPlatformFeePreviewAction extends BaseAction
+{
+    public function __construct(
+        private readonly GetPlatformFeePreviewHandler $handler,
+    )
+    {
+    }
+
+    public function __invoke(Request $request, int $eventId): JsonResponse
+    {
+        $this->isActionAuthorized($eventId, EventDomainObject::class);
+
+        $this->validate($request, [
+            'price' => 'required|numeric|min:0',
+        ]);
+
+        $dto = new GetPlatformFeePreviewDTO(
+            eventId: $eventId,
+            price: (float)$request->input('price'),
+        );
+
+        $result = $this->handler->handle($dto);
+
+        return $this->resourceResponse(PlatformFeePreviewResource::class, $result);
+    }
+}
diff --git a/backend/app/Resources/Account/AccountConfigurationResource.php b/backend/app/Resources/Account/AccountConfigurationResource.php
@@ -19,6 +19,7 @@ public function toArray($request): array
             'application_fees' => [
                 'percentage' => $this->getPercentageApplicationFee(),
                 'fixed' => $this->getFixedApplicationFee(),
+                'currency' => $this->getApplicationFeeCurrency(),
             ],
             'bypass_application_fees' => $this->getBypassApplicationFees(),
         ];

diff --git a/backend/app/Resources/Event/PlatformFeePreviewResource.php b/backend/app/Resources/Event/PlatformFeePreviewResource.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace HiEvents\Resources\Event;
+
+use HiEvents\Resources\BaseResource;
+use HiEvents\Services\Application\Handlers\EventSettings\DTO\PlatformFeePreviewResponseDTO;
+
+/**
+ * @mixin PlatformFeePreviewResponseDTO
+ */
+class PlatformFeePreviewResource extends BaseResource
+{
+    public function toArray($request): array
+    {
+        return [
+            'event_currency' => $this->eventCurrency,
+            'fee_currency' => $this->feeCurrency,
+            'fixed_fee_original' => $this->fixedFeeOriginal,
+            'fixed_fee_converted' => $this->fixedFeeConverted,
+            'percentage_fee' => $this->percentageFee,
+            'sample_price' => $this->samplePrice,
+            'platform_fee' => $this->platformFee,
+            'total' => $this->total,
+        ];
+    }
+}
diff --git a/backend/app/Services/Application/Handlers/EventSettings/DTO/GetPlatformFeePreviewDTO.php b/backend/app/Services/Application/Handlers/EventSettings/DTO/GetPlatformFeePreviewDTO.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace HiEvents\Services\Application\Handlers\EventSettings\DTO;
+
+use HiEvents\DataTransferObjects\BaseDataObject;
+
+class GetPlatformFeePreviewDTO extends BaseDataObject
+{
+    public function __construct(
+        public readonly int   $eventId,
+        public readonly float $price,
+    ) {
+    }
+}
diff --git a/...end/app/Services/Application/Handlers/EventSettings/DTO/PlatformFeePreviewResponseDTO.php b/...end/app/Services/Application/Handlers/EventSettings/DTO/PlatformFeePreviewResponseDTO.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace HiEvents\Services\Application\Handlers\EventSettings\DTO;
+
+use HiEvents\DataTransferObjects\BaseDataObject;
+
+class PlatformFeePreviewResponseDTO extends BaseDataObject
+{
+    public function __construct(
+        public readonly string  $eventCurrency,
+        public readonly ?string $feeCurrency,
+        public readonly float   $fixedFeeOriginal,
+        public readonly float   $fixedFeeConverted,
+        public readonly float   $percentageFee,
+        public readonly float   $samplePrice,
+        public readonly float   $platformFee,
+        public readonly float   $total,
+    ) {
+    }
+}
diff --git a/backend/app/Services/Application/Handlers/EventSettings/GetPlatformFeePreviewHandler.php b/backend/app/Services/Application/Handlers/EventSettings/GetPlatformFeePreviewHandler.php
@@ -0,0 +1,94 @@
+<?php
+
+namespace HiEvents\Services\Application\Handlers\EventSettings;
+
+use Brick\Money\Currency;
+use HiEvents\DomainObjects\AccountConfigurationDomainObject;
+use HiEvents\Repository\Eloquent\Value\Relationship;
+use HiEvents\Repository\Interfaces\AccountRepositoryInterface;
+use HiEvents\Repository\Interfaces\EventRepositoryInterface;
+use HiEvents\Services\Application\Handlers\EventSettings\DTO\GetPlatformFeePreviewDTO;
+use HiEvents\Services\Application\Handlers\EventSettings\DTO\PlatformFeePreviewResponseDTO;
+use HiEvents\Services\Infrastructure\CurrencyConversion\CurrencyConversionClientInterface;
+
+class GetPlatformFeePreviewHandler
+{
+    public function __construct(
+        private readonly AccountRepositoryInterface        $accountRepository,
+        private readonly EventRepositoryInterface          $eventRepository,
+        private readonly CurrencyConversionClientInterface $currencyConversionClient,
+    )
+    {
+    }
+
+    public function handle(GetPlatformFeePreviewDTO $dto): PlatformFeePreviewResponseDTO
+    {
+        $event = $this->eventRepository->findById($dto->eventId);
+        $eventCurrency = $event->getCurrency();
+
+        $account = $this->accountRepository
+            ->loadRelation(new Relationship(
+                domainObject: AccountConfigurationDomainObject::class,
+                name: 'configuration',
+            ))
+            ->findByEventId($dto->eventId);
+
+        $configuration = $account->getConfiguration();
+
+        if ($configuration === null) {
+            return new PlatformFeePreviewResponseDTO(
+                eventCurrency: $eventCurrency,
+                feeCurrency: null,
+                fixedFeeOriginal: 0,
+                fixedFeeConverted: 0,
+                percentageFee: 0,
+                samplePrice: $dto->price,
+                platformFee: 0,
+                total: $dto->price,
+            );
+        }
+
+        $feeCurrency = $configuration->getApplicationFeeCurrency();
+        $fixedFeeOriginal = $configuration->getFixedApplicationFee();
+        $percentageFee = $configuration->getPercentageApplicationFee();
+
+        $fixedFeeConverted = $this->convertFixedFee($fixedFeeOriginal, $feeCurrency, $eventCurrency);
+
+        $platformFee = $this->calculatePlatformFee($fixedFeeConverted, $percentageFee, $dto->price);
+
+        return new PlatformFeePreviewResponseDTO(
+            eventCurrency: $eventCurrency,
+            feeCurrency: $feeCurrency,
+            fixedFeeOriginal: $fixedFeeOriginal,
+            fixedFeeConverted: round($fixedFeeConverted, 2),
+            percentageFee: $percentageFee,
+            samplePrice: $dto->price,
+            platformFee: $platformFee,
+            total: round($dto->price + $platformFee, 2),
+        );
+    }
+
+    private function convertFixedFee(float $amount, string $fromCurrency, string $toCurrency): float
+    {
+        if ($fromCurrency === $toCurrency) {
+            return $amount;
+        }
+
+        return $this->currencyConversionClient->convert(
+            fromCurrency: Currency::of($fromCurrency),
+            toCurrency: Currency::of($toCurrency),
+            amount: $amount
+        )->toFloat();
+    }
+
+    private function calculatePlatformFee(float $fixedFee, float $percentageFee, float $price): float
+    {
+        $percentageRate = $percentageFee / 100;
+
+        $platformFee = $percentageRate >= 1
+            ? $fixedFee + ($price * $percentageRate)
+            : ($fixedFee + ($price * $percentageRate)) / (1 - $percentageRate);
+
+        return round($platformFee, 2);
+    }
+}
diff --git a/backend/app/Services/Domain/Order/OrderApplicationFeeCalculationService.php b/backend/app/Services/Domain/Order/OrderApplicationFeeCalculationService.php
@@ -14,8 +14,6 @@
 
 class OrderApplicationFeeCalculationService
 {
-    private const BASE_CURRENCY = 'USD';
-
     public function __construct(
         private readonly Repository                        $config,
         private readonly CurrencyConversionClientInterface $currencyConversionClient,
@@ -64,12 +62,14 @@ private function getConvertedFixedFee(
         string                           $currency
     ): MoneyValue
     {
-        if ($currency === self::BASE_CURRENCY) {
+        $baseCurrency = $accountConfiguration->getApplicationFeeCurrency();
+
+        if ($currency === $baseCurrency) {
             return MoneyValue::fromFloat($accountConfiguration->getFixedApplicationFee(), $currency);
         }
 
         return $this->currencyConversionClient->convert(
-            fromCurrency: Currency::of(self::BASE_CURRENCY),
+            fromCurrency: Currency::of($baseCurrency),
             toCurrency: Currency::of($currency),
             amount: $accountConfiguration->getFixedApplicationFee()
         );

diff --git a/backend/app/Services/Domain/Order/OrderPlatformFeePassThroughService.php b/backend/app/Services/Domain/Order/OrderPlatformFeePassThroughService.php
@@ -11,8 +11,6 @@
 
 class OrderPlatformFeePassThroughService
 {
-    private const BASE_CURRENCY = 'USD';
-
     public const PLATFORM_FEE_ID = 0;
 
     public static function getPlatformFeeName(): string
@@ -37,12 +35,14 @@ public function isEnabled(EventSettingDomainObject $eventSettings): bool
     }
 
     /**
-     * Calculate platform fee that exactly covers Stripe's application fee.
+     * Calculate the platform fee line item to show on the buyer's invoice.
      *
-     * Formula: P = (fixed + total * r) / (1 - r)
+     * Uses gross-up formula: P = (fixed + total * r) / (1 - r)
      * Where r = percentage rate, P = platform fee
      *
-     * This ensures: Stripe fee on (total + P) = P
+     * This ensures that when the platform fee (P) is added to the order total,
+     * the resulting Stripe application fee calculated on the new total equals P.
+     * In other words: application_fee(total + P) = P
      */
     public function calculatePlatformFee(
         AccountConfigurationDomainObject $accountConfiguration,
@@ -75,13 +75,14 @@ private function getConvertedFixedFee(
     ): float
     {
         $baseFee = $accountConfiguration->getFixedApplicationFee();
+        $baseCurrency = $accountConfiguration->getApplicationFeeCurrency();
 
-        if ($currency === self::BASE_CURRENCY) {
+        if ($currency === $baseCurrency) {
             return $baseFee;
         }
 
         return $this->currencyConversionClient->convert(
-            fromCurrency: BrickCurrency::of(self::BASE_CURRENCY),
+            fromCurrency: BrickCurrency::of($baseCurrency),
             toCurrency: BrickCurrency::of($currency),
             amount: $baseFee
         )->toFloat();

diff --git a/backend/database/migrations/2026_01_30_000000_add_currency_to_application_fees.php b/backend/database/migrations/2026_01_30_000000_add_currency_to_application_fees.php
@@ -0,0 +1,39 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        DB::table('account_configuration')
+            ->whereNotNull('application_fees')
+            ->get()
+            ->each(function ($row) {
+                $fees = json_decode($row->application_fees, true);
+                if ($fees && !isset($fees['currency'])) {
+                    $fees['currency'] = 'USD';
+                    DB::table('account_configuration')
+                        ->where('id', $row->id)
+                        ->update(['application_fees' => json_encode($fees)]);
+                }
+            });
+    }
+
+    public function down(): void
+    {
+        DB::table('account_configuration')
+            ->whereNotNull('application_fees')
+            ->get()
+            ->each(function ($row) {
+                $fees = json_decode($row->application_fees, true);
+                if ($fees && isset($fees['currency'])) {
+                    unset($fees['currency']);
+                    DB::table('account_configuration')
+                        ->where('id', $row->id)
+                        ->update(['application_fees' => json_encode($fees)]);
+                }
+            });
+    }
+};
diff --git a/backend/routes/api.php b/backend/routes/api.php
@@ -61,6 +61,7 @@
 use HiEvents\Http\Actions\Events\UpdateEventStatusAction;
 use HiEvents\Http\Actions\EventSettings\EditEventSettingsAction;
 use HiEvents\Http\Actions\EventSettings\GetEventSettingsAction;
+use HiEvents\Http\Actions\EventSettings\GetPlatformFeePreviewAction;
 use HiEvents\Http\Actions\EmailTemplates\CreateOrganizerEmailTemplateAction;
 use HiEvents\Http\Actions\EmailTemplates\CreateEventEmailTemplateAction;
 use HiEvents\Http\Actions\EmailTemplates\UpdateOrganizerEmailTemplateAction;
@@ -376,6 +377,7 @@ function (Router $router): void {
         $router->get('/events/{event_id}/settings', GetEventSettingsAction::class);
         $router->put('/events/{event_id}/settings', EditEventSettingsAction::class);
         $router->patch('/events/{event_id}/settings', PartialEditEventSettingsAction::class);
+        $router->get('/events/{event_id}/settings/platform-fee-preview', GetPlatformFeePreviewAction::class);
 
         // Capacity Assignments
         $router->post('/events/{event_id}/capacity-assignments', CreateCapacityAssignmentAction::class);