Custom validations Based on Conditions

Summary:

Would like to create custom validations in the Redwood Edit Purchase Requisitions page based on certain conditions

Content (please ensure you mask any confidential information):

E.g.  

 if ($fields.purchaseRequisitionsLine.DestinationType === 'Expense') {      return true;    }

then would like to add a custom message at the the time of Save or at the time of Submit the page.

However, it is not validating the condition and not stopping.

Version (include the version you are using, if applicable):

26B

Code Snippet (add any code snippets that support your topic, if applicable):