Made a mistake of my application fees

Hi,this is a stupid mistake. I knew the fee was up yet I didn't check and sent it straight away. So I've authorised the old fee instead of the new fees. My question is what will the Home Office do? Return my documents or rejected?

Thanks for your help.

The will most likely return it or ask to pay the difference.

They will probably write to you and ask you to pay the difference of £99 before being able to proceed with your application. Another user recently had this happen and he had 14 days to make the additional payment.