I have the same problem with one of my external accounts on my iPhone 14 pro max. I was told that it can be manually corrected by calling in during daytime. The apple support staff has to make a three-way call, i.e., you, apple & your external bank to verify you and then they can correct the problem on your iPhone. I want to resolve this issue and I have spent 3.5 hours on this over the phone last week but was not successful. In twice of the calls, the three-way calls was dropped on apple support staff side and leave my bank rep and me were talking. We have to hang up the phone finally without the results and no call backs from Apple support! I think any banks in this situation will call me back immediately to resolve the issues. It was frustrating. I have been an apple customer for many years and this is the worst customer service experience I have had.
As an alternative, I have verified and connected my external bank account to my apple savings from the bank side. I can now send and withdrawal money from my external bank side. But I still want this bank accounts on my iPhone working so I can send and withdrawal money from the iPhone as well. Hope Apple will fix this kind of issue quickly.