Create Post: Image upload not working

Tried 3 times uploading an image during Create Post.

The error message in the bottom left corner: SyntaxError: Unexpected token 'R', "Request er"... is not valid JSON

Edit 1: Also tried uploading an image via the comment section's GUI, but it also fails with the same error message.

Edit 2: Similar to https://github.com/LemmyNet/lemmy-ui/issues/1489

• But not the same as user dcx's comment that it was due to file size greater than 1 meg. The file I'm uploading is 766 KB.
• Tested with 264 KB and 20 KB files, both fail to upload.
• Tested from multiple browsers, upload also fails.