In app purchases not allowed, but settings says otherwise.

I am trying to purchase something within an app, however a pop up comes up saying that in app purchases are not allowed however when I go into the settings it says that they are allowed and no password required, I have tried to turn the purchases off then restarting my phone and then turning the settings back on then restarting again to no avail, I have also tried it with and without requiring a passcode.

Any help would be much appreciated, many thanks.