method not allowed when subscribing to a newsletter

paraphrasing a bug report received by email from @smith

when I click on the confirmation address in your email to me, appears: "Method not allowed" and "Must be one of: OPTIONS"

to reproduce:

1. head to the newsletter page
2. fill your email address and the captch, hit "join"
3. you'll receive an email with a link looking like: https://donate-api.torproject.org/subscription-confirm?token=REDACTED
4. then you'll get "Method not allowed", if you reproduce the bug

In my case, however, I get a "Subscription Confirmed", so I'm not sure what is going on here.

In any case, we're seeing a drastic reductions in the number of new subscribers since at least december 2020, but maybe as far back as november or october 2020.