I can't edit Code Injections - Request rejected

This is the warning I get when trying to edit fields on Code Injections page:

Request was rejected because user is not permitted to perform this operation.

Version: 3.28.0
Account: Me, Owner.

What I’ve tried: Updated to latest ghost version. Logged in/out.

Anyone else have this problem?

Update.
So, I just deleted everything in my input fields and it saves.
If I try and add ANY code it doesn’t save.
So now I have a broken site which is not great.
Adding code the template files for now :frowning:

I even tried creating a new admin user. That didn’t work either.

More Testing
Hoping this might help someone point me in the right direction…

If I add the following to header or footer - it saves.
<!-- Google Ad Manager -->

If I add any actual scripts like the following to header or footer - it does not save.
<script async src="https://securepubads.g.doubleclick.net/tag/js/gpt.js"></script>

@simonmc can you try in an incognito window or a different browser to eliminate any security/privacy extensions interfering?

Thanks for the suggestion @Kevin.
I tried incognito in Chrome, Safari and Firefox. No luck.

No idea if this helps, but this is the error I get when it fails.

Failed to load resource: the server responded with a status of 403 () https://discover.therookies.co/ghost/api/v3/admin/settings/

Vendor.js: Unhandled Promise Rejection: Error: Request was rejected because user is not permitted to perform this operation.