Attachments mandatory on the Cash Advance creation pages when the employee submits the requests?

Summary:

We wanted to make attachments mandatory on the Cash Advance creation pages when the employee submits the requests.

Content (please ensure you mask any confidential information):

We wanted to make attachments mandatory on the Cash Advance creation pages when the employee submits the requests.
With the help of sandbox we can mark as mandatory, it will just highlight as mandatory but does not insist the user to add attachment. In other words it does not restrict the user. I went through the lot of community docs but still not find the solution for this. Kindly help us suggestion/solutions.