welcome to this moderated Azure community forum.
I'm sorry to read about the changed ingestion constraints, causing the ingestion errors.
Although I understand how the message is constructed, the trailing comma is not valid JSON.
The (JSON) ingestion supports only valid JSON, so this conversion/mapping will not work.
If you are not able to change the logic on the devices, you could try to fix it by adding custom logic in between
the gateway and Azure Data Explorer (eg. An Azure Function or Azure Stream Analytics).
Otherwise, you could ingest the raw data into a dynamic column in a 'source' table and use a Table Update Policy to transform the message.
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