pension contributions

I am struggling to understand how pension contributions tax allowances work. I earn £80000 and have a direct debit for £900 a month to my personal pension provider (so this is taken from my wages after I have paid tax). My pension provider claims 20% apparently and tells me I am contributing £1125 gross. I need to claim as a higher rate tax payer by updating my personal personal payments but what is the amount I put in that box?

Hi,

It would be the gross amount £1125. 

Thank you.