This brings back memories when I participated in the same although I didn't join for merit/s but to have some experience/knowledge and having fun. So the goal is to encrypt a message that only you can decrypt and in order to do that js to use your pgp public key where you have the private one which is used to decrypt what's been encrypted using your public key. I am s little bit confused as to why there's a signed message in OP. Is it another task (fun/blast from the past) if I call it?.
Removed the bitcoin signed message. Finger print placed out of the quote. Hopefully the confusion is not there anymore.
Check your public key, probably missing a or some characters. In the link that you provided, I was able to use people's public key to encrypt message, but I was unable to use yours. Or try and encrypt a message with it to know if the public key is valid or not. If I am not right, let me know.
The public key is good. I think no one should have a problem if he is trying properly.
So nice responses with supporting tools and information are already posted. Good job. When is the first encrypted message I am going to receive?