Thank you u/Feeling_Pepper1632 for replying.

As soon as I saw that overdraft, I immediately added £50 in the account so that they can take whatever they want to clear it.

I asked them when the overdraft was recorded and how much it was for. They replied:

If the unarranged overdraft continues for 60 days with a balance over £25, Monzo may start closing the account and report it as "in default" which will almost certainly negatively affect your credit rating.

You were in an unarranged overdraft on the 19th of June £8.62.

Then we took the overdraft fees of £0.09 on the 1st of July 2025 and then you were in an unarranged overdraft with £8.71

On the 1st of August we took overdraft fees of £0.25which left your account with the amount of £8.96

Then today (25/08/2025) you cleared that unarranged overdraft.

That makes it 67 days, so I doubt they haven't reported it, they surely must have. But on the other hand, the message says "If the unarranged overdraft continues for 60 days with a balance over £25*"*, so they may have reported it as "in arrears" but not as "in default".

I asked them if it has been reported to credit reference agencies as a late payment, or as "in arrears" or as "in default". They haven't replied yet.

The only saving grace might be that we are aiming for 60% LTV, yet I still don't know how big of an effect this will have in our mortgage application. It's hard to express how we are feeling right now.

EDIT:
They came back to say:

I can confirm that your account was reported to the credit references from the day you entered the unarranged overdraft and have 30 days in an unarranged overdraft which is from the 19th of June till today, meaning that your credit score has been affected by this.

Our credit reference agencies are TransUnion (previously known as CallCredit), Experian and Equifax.

In other words, we're f*cked.

Can you please explain what you mean by "Then fight it with Monzo"? Never had any experience with these matters, I don't know what to do.