"Invalid Email address" error when attempting to change account password on iPhond and iPad

I use Gmail. Recently I received an e-mail from Google informing me that my account may have been compromised. I verified this by logging into Google itself where I got the same message: that they had recently blocked an attempt to sign in. The problem is, when examining the login history, it just stated "unknown device" - and did not reveal any IP address. I had no way of telling whether it was actually one of my own devices, or someone else who was attempting to access my account.

I decided to play it safe and change my Google password anyway. So far so good. However, when attempting to change it on my iPhone I encountered a problem. When I tapped "Done", I got a pop-up message

**"Invalid Email addres"**
Please enter a valid email address for this account.

I was unable to save the new password. My e-mail address had not been changed: the only thing I wanted to do was change the password recorded on the account settings. Suspecting that it might be an issue with my iPhone, I tried it on my iPad - with exactly the same result.

The strange thing is that when I typed in my OLD password, it worked (i.e it allowed me to save the settings screen: it did not allow access to mail, because it was the wrong password).

Does anyone know what's going on? Unfortunately I can't include a screenshot from my devices, because I'm unable to e-mail them to myself because of this error. Right now I'm stuck with no access to e-mail on my Apple devices. Grateful for any insights.

Google won't let me revert to my old password because I used it too recently.

I solved this myself - but am posting the answer here in case it is of any use to others.

It's actually a change in how gmail recognises user names. While previously the username had to include the whole e-mail address, with @gmail.com - now it does not have to. So I only had to remove the @gmail.com portion of the username field, and the problem was resolved. The only remaining mystery is why, given the obvious change, it was still working until recently with my own account settings! But that is another question.