HTTP error 500 model XY not available for vendor YZ

[ypsilonkah]

hi,
I am running into the following problem: I have started and setup fabric as a docker container and are exposing ports etc. I can use fabric from inside the container perfectly fine (i.e. connect to container's shell).
I setup the mcp server using open webui's mcpo docker container. The MCP server connects to the dockerized fabric instance. In Open Webui, I setup a tool pointing to the MCPO-instance and the FABRIC MCP server; it connects as it should. I can list patterns, models, vendors, etc. successfully. In the logs I can see the respective calls to fabric's api.

However, when I start prompting in Open webui like "Use fabric's pattern 'create_pattern' to create a pattern from the following input: 'you are a helful...' " I receive the following error message

"error": "HTTP error 500: {\"detail\":{\"message\":\"Unexpected error\",\"error\":\"500: {'message': \\\"Error calling tool 'fabric_run_pattern': Error executing pattern 'create_pattern': Unexpected error executing pattern: Fabric API error: Error: model gpt-4.1 not available for vendor openai\\\"}\"}}"

The error persists, if I specify vendor and/or model to use in the prompt or select a different model and/or vendor (which are configured of course).