Things I found helpful:
- Documentation in bitbucket (small link in D365 component header):730
- Go to base_url/api/data/v9.x/EntityDefinitions?%24select=EntitySetName (found this in error message and in document) to get JSON results of all entity definitions.
- endpoint is simply just the name.. endpoint url will be built for you... e.g. account for account endpoint.
- Query can be empty..this will pull all results. Would be same as using " $select=* "