Validation rule for Text field –
It should be not blank OR if any value already in text field then it should be changed.
Based on two conditions:
- Picklist value should be Rejected
- RecordType.devloperName should be 'RecordUpdate'
I started by writing below rule.
AND ( ISPICKVAL(Status__c,'Rejected') , ISCHANGED(Comments__c) )
If I understand your question correctly, the validation rule should fire based on following conditions:
Then throw the error message.
The rule will be like this: