@Paul Mac The mapping of API versions to SDK is as mentioned below:
SDK Version -> 3.1.X -> API Version -> 2.0,2.1
SDK Version -> 4.0.0-beta.4 -> API Version -> 2.0, 2.1, 2022-06-30-preview
This is documented on this page for reference.
So, using the 4.0.0-beta.4 SDK version is appropriate in your case since you have used API version 2022-06-30-preview for training your model.
With respect to the error, I think this is a model issue in the backend since you are seeing the error with the latest beta SDK version too.
You should be seeing the same behavior with the form recognizer studio too. Did you get a chance to test from the studio?
If this error persists, I recommend trying a different model id in your code and check if it is able to use the client to get a successful result.
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