This worked perfectly! I was skeptical because if you dump the $form before submitting there are hidden fields already that don't get sent, so just adding another hidden field didn't make sense that it would work when others didn't. You should rewrite your comment as an answer so I can mark it.

Ah that could work, I’ll try that later and see if it submits. Thanks!

That dump is from my external site within $_REQUEST.

Yes sorry should have included that. I can use that no problem. However storing that information where it is added to post is a problem. Seems that add to cart only submits some information and not all the form data.

Thanks everyone! I think I am going to move this over to Software Recommendations as I can't think of a good way to word this while keeping within the guidelines.

Looks like Nov 2021, yeah that is eventually the plan though I need to learn the new D8 module structure. Also it's hard to be convinced to migrate to a version which I find primarily has alpha state modules.

Fair enough, not sure which Stack site this would be OK at then.

How is it off topic if it's specifically referring to Drupal? But thank you for sharing Tome, wish it was for 7 though.

Sure thing Berta, image added.

well look at that lol. By removing the basic page relationship, and setting the filter to basic page, and keeping the relationship for the fields. it works! You should add an Answer below so I can mark it for you.