Description of my issue:
Fails at Dropbox upload. Attempting transfer of completed archive gets message:
Upload of your archive failed. The upload session cannot be created.
Debug info:#500 - invalid JSON Data.
Scrolling down, I see:
Error (4xx)
We can't find the page you're looking for. Check out our Help Center and forums for help, or head back to home.
This is configured to use Upload to Dropbox (v2 API) and a chunk size of 10. The archive file itself is 616.08MB.
This used to be successful some time ago, and using the older API, but I am not sure what has changed. Transfer of the database alone (47MB) is successful, so it very likely has to do with size, though that is still using v1 API. The full site failed with the v1 API also.