A mistake is a new row
A teller posts 50,000 to the wrong member. The useful fix is not to open yesterday and type 20,000 over it. The book would then claim that 20,000 was what happened at the counter, and the receipt would be a lie.
Daybook refuses the edit. The teller posts a reversal. The wrong member’s balance goes back. A new row records the right amount, if money is still to be posted. Both rows stay. Anyone who asks can see the mistake and the correction.
The same rule covers a move between cash, bank, and mobile money. If the transfer was written to the wrong pot, reverse it and write the move you meant.
This is slower for one minute and calmer for the audit. A SACCO that can change a posted figure cannot explain its cash. A SACCO that can only add a row can.