Sharp ER A-280F cash register locked

You need to check the mode switch
It can be turned on by inserting one of the two provided mode keys - director key (MA) or operator key (OP). These keys can only be inserted or removed when the mode switch is in the "REG" (recording) position or the position indicated by a sort of circle with a small line, as this mode locks all operations of the cash register. (The power supply is turned off). No changes occur in the cash register data.

Otherwise, you need to contact the company that services your cash register.

Hello,

What's blocked? The paper? Or the entire cash register?

Hello, the cash register herself.