how to pay on niki through payzapp

hi

i have a niki and payzapp app on my iphone. i am using niki bot to make payment of my electricity bill everything goes smooth and i select payzapp option to make payment, i have adequate balance in my payzapp account to make payment of bill, but when i select pay by payzapp option on niki app it just takes me to some payzapp and ask me to enter debit or credit card details, it is not integrating my existing payzapp app and picking balance amount from there to pay the bill, can anyone advise me where am i going wrong, thanks in advance.