Our NPO is in the process of creating a reimbursement chart for our employees
and we're trying to make it so that if they do not fill in a particular
column entitled "Project," they will get an error message or will be unable
to sum their final expenses together.

Is there a way to make a single column required in an Excel sheet so that
not filling in this cell would block any more entries or would block a final
reimbursement number?

Thank you in advance for any help or advice!