Hey !
That’s interesting. Based on my previous experience, creating an apple wallet pass isn’t something « easy », I mean you’ll hardly be able to do something without using a third party platform.
In your particular case, I suggest you to use Zapier with following softwares, you can then email the pass to your users email, or add a link I’m your google sheet, then retrieve it in the app and finally the user will be able to download it to his/her iPhone.
I’ll keep an eye on this topics, that’s something I’m interested about