Double check all pass / landing-page / email copy for typos and grammar.
Ensure all links on your passes point to the correct pages / resources.
Test your GPS and / or beacon notifications if you have them set up.
Ensure to test the full end to end flows for your users for both Apple Wallet and Google Pay. I would suggest doing this at the starting point for the user, i.e. when they make a purchase on your website or sign up. I strongly recommend doing this for all your use cases (pass issue, update, delete, etc).
Put together a FAQ for your users with questions you anticipate them asking, i.e. where can they find their passes after it's installed, how do they use it, etc.
Create documentation or other video / support assets for your customers to view if they have questions.
Train your operational and support staff and ensure to create awareness within the team that you are launching digital passes within your organization.
If you are implementing a physical redemption process then ensure to test all is working as expected and customer facing staff are aware of the process and can troubleshoot / support customers in case of questions upon checkout.
If you are migrating from our legacy Cherry Pie platform then it's also worth to educate your users on the new pass landing pages - they are slightly different from Cherry Pie and no longer render a full pass preview.