I am using Free Tier option for BTP.
Trying to create API provider for "Slack_workspace_for_orders" with connections settings as follows:

but get an error:

Inspecting the error in Dev tools shows the following response:
{"error":{"code":"INTERNAL_ERROR_OCCURRED","message":{"lang":"en","value":"An internal error occurred, contact SAP administrator for details"}}}
Any ideas what might possibly be wrong?