This is a project designed to capture all information related to Hoppie's ACARS System and document it. The two pieces of material I referred to the most are: ICAO's Global Operation Link Document & FAA's Data Link Services Guidance Material
There are a few examples of libraries/applications you could check out that utilise these formats mentioned & see what's really under the hood
- hoppielib-go My own library written in Golang, to assist developers with linking in easier with Hoppie's ACARS
- EasyCPDLC Application written by Joshua Seagrave in .NET, providing a standalone client to access the ACARS network