My issue is specifically with AUTO-Generated invoices after a contact signs a contract and making them show up under Payments within an opportunity.

I understand you can manually assign any invoice (including auto-generated) to an opportunity. It's also possible to assign a standard invoice to an opportunity if you SEND the invoice from within a workflow.

You can currently add opportunity data to contracts, so it would make sense to simply carry that data over and link the invoice created to that same opportunity.

Support #4022940