@powercat50 - the jetpack contact forms are not built in a way that they will work with popups. I have looked into it but the way they build and submit the forms would require major modification.
Contact Form 7 & Ninja forms both work perfectly for free plugins, and if you want more you can also look at Gravity Forms.
All 3 of those are fully supported and will work out of the box with Popup Maker.
Hope this helps.