Sendy error (Not Connected – provide a valid list ID

I have recently installed Sendy and mailoptin . I am trying to connect mailoptin to my sendy account.

I have entered the Sendy API Key
The Sendy Installation URL
and the email list name and ID.

However, when I click save changes I get an error (Not Connected – provide a valid list id)

I have tried created two different email lists and tried copying and pasting their list ids in multiple times, but I keep getting the error.

I appreciate any help you can provide. mailoptin seems like a great plugin and I am really looking forward to using it.

The page I need help with: [log in to see the link]