The following article has examples of common registration rules and the conditions you should add to create them.
This rule enables you to deny a person from registering for a course if they have not purchased a ticket (optional extra).
For this method to work, the course must have no price. Only the tickets (optional extras) should carry a price.
Initial Screen
Choose which options the rule should be applied to
Add DENY rule
This rule enables you to deny a person from registering for a course if they are using an email address with a public email domain (e.g. forces them to use a work email address).
Initial Screen
Choose which options the rule should be applied to
Add ALLOW rule
If you want to only allow personal email addresses to be used, you can also use the same rule but with is public email domain.