Redeem manually

How/where are you trying to redeem it ? If using your computer's iTunes have you tried on an iOS device instead (or vice versa) : Redeem App Store & iTunes Gift Cards, Apple Music Gift Cards, and content codes - Apple Support ?

What is the 'same page' ? Do you mean that you've tried on both your computer's iTunes and on iOS device ? And are you doing that part manually e.g. opening iTunes on your computer yourself and doing Account > Redeem (or using the Redeem link under Quick Links on the right-hand side of the iTunes store homepage) ; Redeem button at the bottom of the Today tab in the App Store app on an iOS device ? If it's failing on both computer and iOS device are both using the same network, if they are do you have access to a different network that you could try ?

And is that still on the same device/computer, or have you now tried more than one ?