The generic “HTTP error” during uploads usually hides server-side restrictions.
It often results from low PHP memory limits, file size restrictions, or image processing failures.

Check PHP settings like upload_max_filesize, post_max_size, and memory_limit. Image libraries such as GD or Imagick can also cause failures if misconfigured.

Testing with a smaller file helps confirm whether size is the issue.

The common mistake is troubleshooting only within WordPress without checking server limits.
The takeaway is that media uploads are tightly coupled with PHP and server configuration.