Split a GSTR-1 file the portal rejected for size into several files, and get an upload order with the totals to expect after each one.
Your file stays on your computer
GSTR-1 JSON
The portal rejects files over 5 MB. Its line-item cap is quoted as 10,000 in newer guidance and 19,000 in older, so the defaults are cautious. Raise them only if you've checked the current limits.