Thanks for the guide but sadly i dont see any link in Coinbase
"To use the Coinbase sign message feature, go to https://www.coinbase.com/addresses/ and choose the address you want to use, then click "Details" and you'll see the link to sign a message "
Has it been removed?
I didn't see a link either. Though I can't find where I read it I found out that Coinbase no longer supports the signing feature.