Github still asking for credentials despite successful creation of deploy key?

Question

I have created a deploy key according to the windows instructions here

But instead of using the deploy key that has just been set up, git push instead asks for credentials, first with a pop up, then with an SSH pop up, then in the git bash command line itself! This is quite shocking because the whole purpose of a deploy key is to avoid having to provide access to an entire github account

Given I have followed github's own instructions precisely and this isn't working, I am lost as to what to do next.

Notes

• Some time ago, somehow, I set up a deploy key successfully on the same (windows) server. So perhaps the > 1 key on the machine is confusing some part of the process. I am not sure this has anything to do with it though.

• I can see here that github expects keys to be named id_rsa and id_rsa.pub, but given this is my second deploy key running on this particular server, I named the second set differently so as to avoid overwriting the original set (the original set are still there, there are just two more files in C:\Users\[YOUR-USER-NAME]\.ssh\)