A new option has came to Google Pay that lets it automatically, continuously import “passes” (including tickets and loyalty cards) from emails received in Gmail. The option is disabled by default, but is available now for most users within the Google Pay app, under Settings > General > Gmail imports.
Passes added via this feature are marked with a mail icon, and the pass includes a link to the specific email it was generated from. Due note each “pass” will tell you that deleting the email from your Gmail account will also remove it from Google Pay.