API Error Method Not Allowed

[benehudson]

Describe the bug
I reported this bug on the Umbraco GitHub thinking it was an Umbraco issue in v14+...
umbraco/Umbraco-CMS#16964

But, just this morning I had someone on the Umbraco forum say they have the same issue after running uSync. I too am running uSync in my instance. So, I'm wondering if the error I'm getting might be related to uSync.
https://our.umbraco.com/forum/using-umbraco-and-getting-started/114582-v1412-apierror-method-not-allowed#comment-351662

Everything works fine locally in IIS Express, but when I deploy to my IIS server I get "API Error Method Not Allowed" any time I try to save any Content or Settings node in the back office.

To Reproduce
Try to [Save] or [Save & Publish] any Settings or Content node in the back office of v14+ running on an IIS server. The result is a red notification "API Error Method Not Allowed".

Expected behavior
I would expect for the content node to [Save] and/or [Save & Publish]

About your Site (please complete the following information):

• Umbraco Version: This has happened on v14.1.1, v14.1.2 and v14.2
• uSync Version: 14.0
• Browser: Chrome
• My site is a content delivery site, so no view templates.

Additional context
My site was a v9 site. I spun up a new v13 site and used uSync to port the content from v9. I then removed templates and converted it to a Content Delivery site. Then I upgraded from v13 to v14. I don't know if any of this is relevant, but figured every bit of detail might help.

[benehudson]

I just spun up a minimal v14.2 site without uSync and this error still exists. uSync is innocent. Closing this thread.