Can't send email to all contacts, even though they're all set up as marketing contacts

Hi Karsten - many thanks for your reply.

I’ve done everything you suggested, and I’m still getting this error message.

Marketing 3.png

I also can’t update all my contacts in bulk. As you can see below, the “Finish” button is greyed out, and I can’t do anything.

I’m at my wits’ end here. I just don’t know why this is happening.

Any help gratefully received!
Thanks,

Steve Tilling