Deposits initiated via Open Banking transfer method cannot be cancelled on IBKR side. In order to decline/reject the transaction you may use your banking app and follow the prompts to decline/reject, unless the payment was already processed and it is in transit.
Why can I not cancel my Open banking deposit notification?
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Why was my deposit initiated via Open Banking is not received?
Why is my financial institution not available to connect for Open Banking?
Can I fund my account by internet banking?
How do I deposit funds using Open Banking?