I am stuck with this.
Can you please post some picture for more specific.
It's not possible to sign a mesage from Coinbase wallet anymore. They removed this feature several months ago.
I am having the same issue with blockchain.info.... I have searched high and nigh online with little success on how to sign messages. apparently, You can sign from messages from very old addresses but not with the new ones. If anyone has an idea please share. It is ironic that they allow message verification, but wont allow messages to be signed.
I never had issue to sign message with imported adrees on blockchain.info, but never tried to do it with new address. It looks quite strange that don't allow to sign message with all address.
I think not months ago that coinbase sign message is not working last year i can't sign a message of every bitcoin address that is why i stop using their service and use it to deal here in forum because some other people they wanted to sign message first before you deal to someone..
I experienced to sign message in coinbase before but after they change the themes of coinbase the sign message is not working anymore i reported them in coinbase but looks like they have no plan to re-enable it back again. .
Blockchain are good wallet but now a days because of segwitx2 and other fork about bitcoin i think they are not allowed to sign message again for new bitcoin address just for security purposes..