Problem with Relationship and File fields on GoDaddy - 403() error

Hello. I’ve been upgrading a site, updating AddOns, making some tweaks, etc. and the new version is running on EE 4.3.8 (PHP 7.2.32) - works well locally and on my personal staging site, but when uploaded to GoDaddy, the Relationship fields on admin pages never load, just show the animated “Loading…” band. I also had a similar issue with File fields. Also, when I go to try and create a new field in the Control Panel admin, the Type pulldown doesn’t populate.

I get a “failed to load resource:… 403()” error for admin.php:1 which doesn’t appear on my other host.

Any thoughts? I need to make the site live now that the work is complete!

Thanks.