REST API call returns values from one table, but how would one handle relationships?

Just to use a simple example, I’m using REST as a resource, and it retrieves a list of Opportunities from another CRM system. The problem though is things like Company Name are part of the Companies table, which relate to Opportunities via the id_company field.

If I wanted to have relationships work, would that be something I do in Retool? Or would that be something I need to have the API support on the CRM system? I don’t see any way in the documentation to do an API call that retrieves anything other than either a list of records from one table, or a list of details on one specific record.