This is one of my favorites:
https://news.lettersofnote.com/p/i-am-unable-to-accept-your-...
https://news.lettersofnote.com/p/i-am-unable-to-accept-your-...
Was that obvious from his reply and I missed the point?
I am guessing it must be in the form of "Please accept our letter of rejection" or similar?