Your clients were probably mailed debit cards and did not recognize what they were, so tossed them out as junk mail.  IRS told us last month that if people don't claim a recovery rebate credit to which they are entitled, it will be allowed anyway.  So don't claim it on the return -- help them join the long line of people who are asking, "What payment?"  And make sure they don't miss the next big one.  Are they getting a refund?  Are you filing with the direct-deposit information?  (Not that IRS used that when available, last time.)