This has left thousands unable to use the electronic money cards during the Christmas rush, the busiest shopping period of the year.
And those encountering problems with the cards are unable to get through to telephone helplines due to a massive surge in queries.
The market-leading One4all Gift Card is a hugely popular Christmas present, while many companies use the cards to give their staff a tax-free bonus at this time of the year.
Hundreds of companies have opted for the cards this year to reward staff for their efforts during the pandemic.
The company benefits from a tax break that allows employers to give tax-free bonuses of up to €500 a year to each worker if the money is transferred through a gift card rather than in cash.
Anti-money laundering rules mean that if the cards have a value of more than €150 they have to be verified online before they can be used.
Dozens of people have taken to social media to criticise problems activating the cards.
Angry customers have complained of “serious customer service issues” trying to activate the chip and pin cards.
One person on Twitter said she was trying to activate the card to do her Christmas grocery shopping but the One4All website keeps crashing when she tries to do this.
“And I keep getting cut off when I call customer service,” she said.
Others said the phone lines of the card provider were not being answered.
Some people said they were waiting days for gift cards to be delivered to them.
One person claimed the company was not responding to multiple emails, and claimed the customer service from the card provider was “horrendous”.
The company that issues the cards said it has experienced an increase in the volume of sales of One4all Gift Cards this year.
“Employers and businesses have recognised the phenomenal efforts employees have made during the year and are rewarding their employees with gift cards, many of these businesses purchasing One4all Gift Cards for the first time to express their gratitude.”
It said that EU anti-money laundering legislation means photo identification is needed for e-money gift cards with values between €150 and €500.
“This extraordinary increase in the volume and value of gift cards purchased by employers to reward their employees means the processing of gift cards is naturally taking a little longer.”
One4all said: “We appreciate our customers’ patience as we respond to each and every enquiry.”
The company behind the gift card scheme was valued at €100m when An Post sold its controlling stake in 2018. It is now owned by Blackhawk Network, a global financial technology company based in the state of California.