I've used this app for some time now. When I first set it up, the guidance was miserable because they didn't state anywhere that you have to use a personal account login which has to be tied to your business account. A support agent admitted to me that they were inundated with setup issues, especially that one because it wasn't documented anywhere.
Got over that hurdle and have used it since for quite some time with only the usual problems that sometimes the notifications take a few minutes to arrive or sometimes just don't. I've managed.
The latest is that it's just stopped working, can't get past the login button. Fairly tech savvy, have tried all the known steps, support have got me to run through them multiple times and I've been promised a callback from their tech team for weeks now, having provided as clear information as I can, screenshots, software versions, the works. Essentially, I can't use my business credit card to purchase anything online. They have no alternative mechanism like SMS.
The whole roll-out seems to have been done in a rush job, despite PSD2 requirements on 2 factor authentication being flagged well in advance. Poorly rolled out and it continues to be under resourced.
I've set up a Revolut business account and will be shutting down my AIB credit card.