403 Forbidden REST interOrganizationParameters

Summary:

A partner is using an extension to integrate with Fusion SCM. Specifically they want to perform a check on interorganization parameters.

My user (with setup and seeded roles) can go in and call the REST

But our test user with custom roles that minimize access to screens, gets the 403 Forbidden that points to privilege restriction. The question is, which one.

This seems like a search for a needle in a hay stack …

Note: we already assigned the most obvious one; View Interorganization Destination Organization List of Values Web Service

But still no success. And makes me believe it could need access to FSM with privilege like: Manage Interorganization Parameter