It looks like a custom app can only create one Carrier Service.
Topic summary
Main issue: Attempts to add more than one shipping rate provider in a Shopify app return an error: {“errors”:{“base”:[“Shipping Rate Provider is already configured”]}}.
Clarification: A user notes that a custom app can only create one Carrier Service (Shopify’s shipping rate provider entity used to return real-time shipping rates at checkout).
Implication: The error likely indicates a platform limitation—only one Carrier Service per custom app—and occurs when trying to create a second provider.
Status: No official confirmation or workaround provided in the thread; discussion remains open.
Suggested next steps: Check if a Carrier Service already exists for the app and update/manage that single service rather than attempting to create additional ones.