Did you move the database with mysqldump and mysql? Then trigger can fail because he has rights in the old database, and not in the new. The solution is to recreate all triggers. This can be done with the following command.
wp eval "Civi::service('sql_triggers')->rebuild(NULL, FALSE);"
I'm also facing this problem (CiviCRM 5.3.0, WP 5.6.1, Avada 7.2.1).
Disabling the Fusion Builder (so working with the regular WP editor) for the page where the CiviCRM-shortcode is inserted gets the resources loaded and the payment form working.
We're still facing Avada layouts issues on the next page ...
There's a feature I wrote for Email API for use with CiviRules called "send email to a related contact". I haven't looked at it recently to see if you can specify "any relationship" as opposed to a specific one, but it should get you most of the way to a solution.