I try to add passwords to the "pass" password manager. But my attempts fail with "no public key" GPG errors. Why?

How did you create the password store? pass init "Kelly's Passwords"? If so, this is wrong, you should have called pass init 64290B2D.

And if then pass insert foo will fail with:

gpg: fooo: skipped: public key not found
gpg: [stdin]: encryption failed: public key not found

then you have to trust your own key first (gpg --edit-key 64290B2D, trust, 5, save).

With the same indications, if anyone stumbles across this issue, the solution may be bit different. Your pass is using gpg2 instead of gpg, you might have used to generate/manage your keys (or, vice-versa). Verify with:

bash -x $(which pass) insert foo

I got the same error for while, running the bash in debug is helping. ( bash -x ), I then realized that pass had listed a non-existing gpg-key in .password-store/.gpg-id