Unable to insert blog

I’m trying to add one of my old sites (which Im sure used to be linked via Jetpack but isn’t anymore), and when I click to ‘Set up Jetpack’ I get the following error:

{‘code’:’insert_blog’,’message’:’Unable to insert blog. Please try again or contact support.’,’data’:400}

On the support pages (https://jetpack.com/support/getting-started-with-jetpack/what-do-these-error-messages-mean/) it tells me “This error means there’s an issue with the way your site’s URL has been stored in our system. This is something we’ll need to fix on our end. Please?get in touch with support?for help.” but the linked page just tells me to ask in the forum.

Is this something anyone can help with? Or any idea of someone I can contact?