Check how to retrieve invoice/receipt details by the partner service account

Once invoice is linked -> we need to support the retrieval using the partner service account

No files, tests, or entry points are named. Clarify how the invoice is linked, which partner service account should retrieve it, and the expected response or permissions, then trace the existing invoice retrieval flow. Done means the required details can be retrieved through the partner service account and the behavior is covered by appropriate tests.

Written by the indexing model from the issue text.