Studio REST Proxy returning 401 when calling Shared Flow

Trying to trigger a common module from multiple inbound flows using the REST proxy. Token generation looks fine in the setup step, but the POST to the flow execution endpoint fails.

ASSIGN proxy = GetRESTProxy(“common-module”)
ASSIGN result = proxy.POST(“/api/v2/flows/executions”, {“flowId”: “xyz-123”})

Getting a 401 Unauthorized. The token expiry is set to 3600s, so it shouldn’t be stale. Is there a specific scope missing for cross-flow calls?