See the several topics on Naira like Subscription in USD - #3 by eko
You can pay as you did from a US$ account as CBN does not allow Naira cards to be used for payments outside of Nigeria. Manager thus can not accept payments in Naira and therefore @Lubos should look into not displaying an amount based on local currencly if users can not pay him in that currency. So should for IP addresses that originate from Nigeria and similar countries to a USD or GBP price and payment method. It is a sad situation but one can not blame Manager for not being able to be paid in Naira, it is a CBN thing.