Could not save uploaded file! Error
If you cannot upload a plugin or a theme to your Favorites extension and get the Could not save uploaded file, it is more than likely that the tmpfile() PHP function is disabled by your host.- Go to the MainWP > Status > Server Information page
- Find the Disabled Functions check
- Verify that the tmpfile() PHP Function is disabled by your host
- If yes, contact your host support and have them enable it for you.
Source Article:
https://kb.mainwp.com/docs/could-not-save-uploaded-file-error/