Payloom3 and Stacks problem?

I have a Payloom3 page with products and prices etc inputed. I’ve created a Stacks 3.0.1 page and added the Payloom 3 Remote Stack, and then pasted the Payloom 3 page URL into the correct place. But when published I’m not getting the Payloom page as expected but an error page from a previous project? I’ve tried and checked everything that I can think of, and now just stuck?

This is the page:

What am I doing wrong? Thanks for any help.

Might be some legacy errant page sticking it’s nose in.

Certainly a contender for re-publish all pages.
Likely a contender for wiping the sever and a clean re-publish. (Obvious caveats of backing up and saving server files apply).