Your balance is always displayed on the main page, "Main account" widget:
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It gets automatically updated after each transaction. You can check your transaction history on the left side of the main page if you are using 1ST OPUS web version:
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Once you do it, the transactions history will appear on your screen:

If any transactions cause the balance in your Card Account to go negative, including any purchase transactions where the retailer or merchant does not request authorization, you shall remain fully liable to us for the amount of any negative balance and any corresponding transaction fees.

You may also be liable for any related Insufficient Funds/NSF Fee(s). We reserve the right to bill you for any negative balance or to recoup such negative balance from any other Card we have issued to you. You agree to pay us promptly for the negative balance and any related fees. We also reserve the right to cancel your Card if you create one or more negative balances with your Card.