Payment due end of July

The HMRC app said I was due X amount by July this year which I have now paid. Now my account shows as "you have nothing to pay" You are in credit X. This is the same as your next payment and will be paid by 30 July 2024. I thought the deadline for self assesment is always 31st January so why was it even asking for a payment in July?

Hi Paul Sheraton,
The amount requested will most likely have been your 2nd Payment on Account for 23/24.
You can find out more about Payments on Account here - Understand your Self Assessment tax bill
Thank you.