There is no “batch” model. This is OpenAI screwing up with the same symptom as has been seen before.
You can try both the gpt-4o-mini name and the dated version.
There is probably some backend translation of the name you use to the one that gives a discount internally, and it is either something about the project or something about the batch API.
You can try making a new API key or new project, and see if your rights to some secret model alias you can’t call directly is turned on.