Bulk Export 400 on Digital Channel Transcript Metadata

Can anyone clarify why POST /api/v2/bulkexports/exportjobs returns 400 Bad Request when including transcript_data for webchat interactions in BYOC EU-West-1.

The error message states ‘Invalid filter: transcript_data is not supported for channel type webchat’. We need the full transcript text for legal discovery requests, not just the media files. Standard call recordings export to S3 without issue, but digital channels fail validation on the metadata schema. Using Python SDK 2.5.1. The job payload matches the documentation for voice channels exactly, which makes this restriction unclear. Is this a known limitation for webchat in the current API version, or is there a workaround to include the text payload in the export job?