"The response is not a valid JSON response."

Hosted on bare metal.

- Did fresh install on Yunohost.
- Installed a theme, Kadence
- tried to embed a video file (mp4, 47 MB) but get this error: "The response is not a valid JSON response."

I thought maybe the upload limit was too small so I downloaded a plugin to increase the file size. It still failes.

I uploaded a PDF file to test that uploads are working.