Of course you must write down the application number, otherwise how would you know which patent you paid for, "application number + fee name (or abbreviation)".
Notes on payment:
(1) When remitting money through the post office or bank, the correct application number or patent number and Fee name. The correct application number or patent number should be 9 digits (patents applied before October 1, 2003) or 13 digits (patents applied after October 1, 2003), and must not be missing, before the last check digit. The decimal point can be omitted.
For example: the 9-digit application number can be written as 9910XXXX.2 or 9910XXXX2; the 13-digit application number can be written as 200510XXXXXX.1 or 200510XXXXXX1. The name of the fee paid may be abbreviated (see Patent Fee Standards).
(2) When the payer pays the patent fee through a bank or post office, the correct application number or patent number and the name (or abbreviation) of the person to whom the fee is paid should be written on the money order. When the payer receives a bank or post office remittance voucher when remitting money, he should carefully check the application number or patent number, as well as the payer's mailing address and postal code. This information will play an important role in subsequent procedures. Fees may not be sent to the Patent Office acceptance office.
(3) Remit money through bank or post office. If you need to send a fax, you should send a copy of the remittance slip together with the application number or patent number, fee name, item amount, postal code, address, and recipient on the day of remittance. Send the recipient information to the toll office. (Fax: 010-62084312). This method is a remedy for failure to indicate the above necessary information when remitting money, and has no legal effect.