Proof of unearned income

I'm currently applying for Student Finance Wales and they asked me if I have any extra income eg interest from a savings account and they asked me to predict how much I will earn across the 25/26 academic year. I have provided them with the interest rate on my savings account and the amount in it, and how much interest I should be receiving. I have submitted the application and my to do list is asking me to provide proof of unearned income. I have got a bank statement from my account to upload but the only proof options are self assessment tax return, self assessment tax calculations, tax calculations, confirmation from accountant of income from all sources, copy of rent book, copies of dividend statements, or shares. If I check the box that says "I cannot provide any of the above" it just takes me straight back to the beginning and I can't upload any proof. Does anyone have any suggestions on what I can upload? My only proof is a bank statement from the savings account showing the interest rate and the amount of money in there. Any help would be appreciated.