To ensure data integrity where the Region field on the Contact object needs to be filled out conditionally based on the parent Account's status, a validation rule on the Contact is the most effective method:
B . Create a validation rule on Contact. This rule can enforce that the Region field must be filled out for Contacts related to Accounts marked as 'High Priority'.
Steps to create this validation rule:
Navigate to Setup → Object Manager → Contact → Validation Rules.
Create a new validation rule.
In the formula, use:
AND(
ISPICKVAL(Account.Customer_Status__c, 'High Priority'),
ISBLANK(Region__c)
) )
Provide an error message to display when the rule is violated.
Save and activate the rule.
This validation rule checks that if a Contact is associated with an Account marked 'High Priority', the Region field cannot be blank.
For further detail, Salesforce's Validation Rule Considerations provides additional guidance.