If you deposit cash at an ATM and the amount doesn't appear, keep the receipt or take a picture of the error message and note the exact time, location, and amount of the machine.
Steps
Check your account first to make sure the transaction wasn't delayed by a few minutes.
If it still doesn't appear, contact your bank and file a complaint about an unrecorded cash deposit, obtaining a reference number.
Do not make a second deposit as a test before reporting the initial issue.