Font Library Install Fonts not accessible after migrating website

[lukeseager]

I need to test this more to find scenarios where the issue occurs. But at the moment if I make a website locally, then migrate it to a live or staging link, I'm not able to access the Install Fonts tab on the WP Font Library. The editor throws an error.

I have a side-by-side comparison, of the same website with a default theme and no active plugins running, showing that the local site (which was created first), can access Install Fonts, and the staging site, which cannot access Install Fonts.

​https://start2finishmarketing-my.sharepoint.com/:v:/g/personal/luke_seager_s2fmarketing_co_uk/EcEgh7k9qjxNvCF69QJG1rMBZOBm5FgZ8kVdgGAlJyFuCQ?nav=eyJyZWZlcnJhbEluZm8iOnsicmVmZXJyYWxBcHAiOiJPbmVEcml2ZUZvckJ1c2luZXNzIiwicmVmZXJyYWxBcHBQbGF0Zm9ybSI6IldlYiIsInJlZmVycmFsTW9kZSI6InZpZXciLCJyZWZlcnJhbFZpZXciOiJNeUZpbGVzTGlua0NvcHkifX0&e=5B97Hn

In the console, all requests complete with a 200 status and are the same on both local and live/staging sites in terms of requests and responses.

I wondered if the issue was to do with the 'allow access to Google fonts' button that shows the first time you try to Install Fonts, but I don't think this is the case. I deleted a Google Fonts transient from my staging sites database just in case it was related in some way, but it made no difference.

As I say, I need to test more scenarios, but this seems to be a definite scenario where the Install Font view can't be accessed.