Dropbox upload session append - incorrect offset

If the first /2/files/upload_session/append_v2 call is failing with 'incorrect_offset', and indicating a 'correct_offset' of 8024827 for that upload session, then that indicates that the API received that much data for that upload session in the /2/files/upload_session/start call. That is, the 'correct_offset' value indicates how much data the API has received so far for that upload session. If this number is higher than expected, it's likely that your code is accidentally sending more data per call than you intended.

I recommend debugging your code for calling /2/files/upload_session/start to make sure you're only sending as much data as you intended, i.e., "4194304 KB" in this case, from your description. (By the way, did you mean bytes instead of KB? 4 MB = 4194304 bytes, not KB.)

Also, it makes sense that it would work if you use a chunk size of 150 MB for a 20 MB file, since you would be uploading the entire file in the /2/files/upload_session/start call, and so wouldn't need to use /2/files/upload_session/append_v2, so the offset value doesn't need to be checked.