FB50 records a G/L accounting document with equal total debits and credits. A balanced document is necessary, but it isn't enough. Posting repairs to office supplies can leave the overall trial balance unchanged while making both management reports wrong. The account names matter as much as the arithmetic.
An expense line in this training client also needs a valid cost center so the cost can be assigned to a responsible area. Use the posting date in the task, not the date you happen to be working. The reference connects the journal to its source evidence. These exercises post cash expenses with simple balanced lines, then check the account, cost center and amount together.