Which box did you tick when it asked how long you had been earning your salary and whether it had been the same amount continuously or not?
There's an error in the online form, where if you tick the box that says 'not the same amount continuously' or 'below the requirement', it will tell you to provide 12 months of payslips and bank statements, even when you have been either earning above the requirement for more than 6 months, or are combining your income with savings to meet the requirement, and you should only need to send 6 months' worth.
If you did tick that box, and you are able to go back to the question and edit your answer, then if you change it to 'same amount continuously' it should hopefully only ask you for 6 months' worth (though not sure how it handles the the 'below the requirement' part).
If you are not able to change your answer, then just provide 6 months' worth of payslips and bank statements anyway, and maybe include a note/cover letter explaining that you are Category A and therefore only need to provide 6 months.