Comment 1 for bug 1720207

list-keys only lists *local* keys, it does not show the remote keys uploaded to the store (i.e. the one you registered).

You need to have a corresponding local key (private/public keypair) in order do to signing operations, while the store only has the public portion. So even if you could see that "default" is registered in the store, if you don't have the matching private/public pair, you won't be able to do anything with it.

If you don't have the keypair for "default", at this point your only option is to create a new keypair and register it with the store under another name.

This is also related to https://bugs.launchpad.net/snapstore/+bug/1800825.

I'll mark this as won't fix since this behavior, while weird, is by design.