Mullvad "invalid account"

I’m trying to add Mullvad VPN to my GL-AR750S-Ext router. I’m getting an “invalid account” error message upon submitting a profile name as shown in step three here:
No such message appears when I log in to Mullvad in the iOS app or on the Mullvad site.

I’m accessing the internet via an iPhone tethered to the router while logged in to the Mullvad iOS app. Am I behind a VPN on all devices connected to the glinet router?

Can you make sure there is no space in your Mullvad account?

Thanks alzhao. I can’t find anything about checking for “no space” in my Mullvad account. Could you please get me pointed in the right direction for that information?
BTW: I’m still getting an “invalid account” error.

Image is much easier to understand.

The second problem you should pay attention to Mullvad is