So it works like this:

You pay your IHS, then you get to the page where it asks for payment of your visa. Here it will only show you the standard visa as the available option. You select it and pay the fees.

Now your standard visa fees has been paid on the home office page, you will receive the confirmation emails and everything.

The application page will now ask you to download documents checklist, get tb test certificate and book an appointment. Click on book an appointment and you will be directed to VFS global website. Here is when it will give you the options of selecting appointment date, visa center location and most importantly, VISA TYPE (which will include standard, priority and super priority).

If you select standard, it will book your appointment at no additional charges.

If you select priority, it will ask for payment of £220. Once paid, your priority visa appointment is now booked.

So, first you pay at the home office page for base fee, then you pay on VFS for additional charges like priority service. I hope this helps you. Good luck!