I pay for Instagram ads in Nigeria, just the same way I pay for Facebook ads. This is simply because Instagram uses the same powerful advertising tools as Facebook. Hence, I set up, run and track Instagram campaigns in the same way as for Facebook adverts.
So, if you're already using Facebook ads, just go ahead and create your ad, link your Facebook page to your Instagram account and when you get to the "placement" section, select "Instagram". Payments for your Instagram ads will be deducted from the payment methods you've added to your Fb ad account.
If you are new to Facebook advertising, you can get started with Instagram advertising and pay for your Instagram ads in Nigeria by making use of PayPal, a dollar card issued by a Nigerian bank, Payoneer MasterCard or by making use of the PayU payment method (for Naira Fb ad accounts).
You can access the Facebook payment methods page right here. Right there, you can select how you want to pay and add info of your payment method.
On my USD Facebook ads account, I pay for fb ads by making use of my GTBank dollar card, my Payoneer Mastercard and my PayPal account linked to my GTB dollar card.
On my Naira Facebook ads account, I simply make use of the Pay with PayU method to add funds to the Facebook ads account.