How can I find changes to REST API's in Fusion Financials for a monthly or quarterly upgrade

Evidently we are using a REST API in a Receivables invoicing process. In what documentation can I find any changes happening to REST API's or also SOAP web calls in an upgrade? It's possible we don't have the correct versioning setup in our process; when there was a change to one of the API's in 26C, we had issues. We can look at correcting the versioning in our code to hopefully prevent this going forward, but it would also be helpful to know what is changing so we can focus our testing. Since this happened in