For RestLink calls you must edit the C:\ProgramData\Eclipse\DatalinkExecutables\CallDefinitions.json file.

Your datalink name must match a method exactly.

If using a different environment then a different ERPLogin method must be setup to the new server. This also needs a new datalink with the same name.
The  "AuthParameter":"bWFuYWdlcjptYW5hZ2VyMSE=" value in the ERPLogin method is username:password encoded to base 64 using https://www.base64decode.org/

Calls can be checked in swagger to make sure they complete and return what is expected.
https://v-dev-app2/EpicorERPTSDev/api/v1/Erp.BO.APInvoiceSvc/APInvoices('T130',12,14598)

Main swagger link. (adjust for different servers or instances)
https://v-dev-app2/EpicorERPTSDev/API/help/v1/