Hey @Oigres,
We have a separate section for batch transform in the documentation, which contains a YT video and a sample notebook. The notebook shows how you can create the jsonl file for your batch transform.
As far as I know, batch transform works like that, SageMaker is sending each “line” of the jsonl as a normal HTTP Request to the inference toolkit. Meaning each line should be a valid JSON document. so true should be correct.
Could you share your cloudwatch logs? Maybe they are more saying about the error?