Technical faults meant that for several hours on Tuesday, some Bank of Ireland customers could withdraw large sums from cash machines despite having little or no funds in their accounts.
Pictures and videos shared on social media showed long queues at machines in the Republic of Ireland.
The bank said it had been experiencing technical faults, but on Wednesday morning it said the issues had been resolved.
It warned transfers and withdrawals would still be applied to customers’ accounts.
A spokesperson said on Wednesday morning that the bank’s app and 365 Online banking services were now working again.
The issues also affected customers in Northern Ireland, but the bank said “we didn’t have similar reports of customers using Northern Ireland ATMs late last night”.
It added that overnight payments to accounts might appear throughout Wednesday.
“We are aware that the technical issue meant some customers were able to withdraw or transfer funds above their normal limits,” the spokesperson said.
“These transfers and withdrawals will be applied to customers’ accounts today.”
“We urge any customer who may find themselves in financial difficulty due to overdrawing on their account to contact us.”
The bank apologised for the disruption caused.