Field help (REGCODE) 

Enter or select a code consistent with the register type. That is, a petty cash (GESCAI) code for a cash register or a bank code (GESBAN) for a bank register.
If you enter a code that is already linked to an open cash register, you receive a blocking error: “There is an opened register for this Cash register code.”Only one code can be assigned to one open cash register at a time. For example, if you have a petty cash code, PCABC, it can only be assigned to one, open cash register. When that cash register closes, the same code, PCABC, can then be assigned to another cash register.
However, the same bank code can be assigned to multiple bank registers. You can open multiple bank registers, but they need to start from the previous code.