Posting moves each journal line into the relevant ledger account. A T-account shows the same logic with debits on the left and credits on the right. Keep an opening balance on its original side, add the new postings, and subtract the smaller side from the larger one. A credit-balance account is not automatically an error.
Reference letters link the two sides of a transaction. They matter when several entries share an amount. A settled payable may end at zero, and an overdrawn bank can end with a credit balance. Neither balance calls for a plug. Check each account and then confirm that the combined ledger still has equal debits and credits.