Bitbucket's help says:
if your account's username is happy_cat, you would need to create a new account with a username of happycat to use this feature
That's my case, so I created a second account so that I can use the feature.
PROBLEM: I can't use this account with my SSH key, I am told:
Someone has already registered that SSH key.
Using several SSH keys is a pain... is there a trick to make it work with the same SSH key?
(The exact same problem happens with Github)
