HA Cloud - error when trying to create account or sign in - Help please?

Hi, I hope someone can help me, please.
I’m trying to set up the HA Cloud to use with Alexa/Amazon Echo. When I try to set up a Cloud account, or to sign into one I created earlier, I get this error:
Unexpected error: User pool client 3k755iqfcgv8t12o4pl662mnos does not exist.

What does this mean, how to get it to work?
TIA
Andrew