Initial checklist

• I understand this is a bug report and questions should be posted in the Community Forum
• I searched issues and couldn’t find anything (or linked relevant results below)

Link to runnable example

No response

Steps to reproduce

1. Running a similar setup to this: withCustomEndpoints.html

2. Setting shouldUseMultipart: true,

3. Uploading a file > 5 MB - everything works as expected

4. Uploading a file < 5 MB - upload fails.

It was working correctly in Uppy v2, I recently upgraded to v4 and found this issue.

Expected behavior

File uploads successfully

Actual behavior

Upload process goes through signing successfully, but fails when actually uploading a file to pre-signed url.
Error: Non 2xx