Mutt asks "Enter keyID", does not accept any IDs

I am trying to use Mutt with GPG to encrypt emails. Whenever I try to encrypt, I am asked to "Enter keyID for user@domain". No matter what I enter, it asks me to enter the value. I definitely have the key in my keystore. I have entered the full key ID, the 32-bit ID, prefixed it with 0x, added the email, etc, but nothing works. I can also confirm that I definitely have relevant keys in my local store. I do not see an error message. My ~/.muttrc at this point just has the standard gpg.rc that comes with Ubuntu. Am I doing something wrong? Or is this a bug in Mutt? Thanks