The missing access is execute access to the specific Apex class used by the Remote Action. A Remote Action in an Integration Procedure invokes Apex or an invocable action, so the running user must be authorized to execute that Apex class. Salesforce documentation for OmniStudio Apex class permission checkers states that access must be enabled for the classes used by Remote Action APIs for each profile, permission set, or permission set group. “Run Flows” is irrelevant because this is not Flow execution. General data-model access may still be required for object operations, but it does not authorize the Apex class itself. A Try-Catch Block can catch or handle an error response, but it does not fix the underlying unauthorized Apex execution failure.

================