Any ideas on how to to post a sign up form of a FaceBook page, or if it is even possible?
You can try this: https://www.acyba.com/2-uncategorised/435-add-a-signup-form-to-your-facebook-page.html
That link doesn't take you to the correct page anymore
I'm trying to find the answer to this as well
You will have to use a facebook app that allows to add a custom form and use the external subscription form documented here: https://docs.acymailing.com/setup/subscription-to-your-lists/external-subscription
Thank you - but I don't see a Facebook sign up bit
I'm not familiar with Facebook custom tabs, but I do know your page needs at least 2.000 followers to be able to create custom Facebook tabs.