Sign in with your Apple ID - Apple Support
- "When you sign in to the App Store and other media services for the first time, you might need to add a credit card or other payment information."
Apple Account balance alone apparently may not meet the requirement and you need to use another payment method until you find one that satisfies Apple's requirement (often a credit or debit card): Payment methods that you can use with your Apple ID - Apple Support
The list isn't very specific to actual brands and I have no idea what a verve card is. You will just have ot keep trying different ones until you find one that works, or ask a friend if you can use theirs temporarily (you may find you do not need one after you provide one once if all you want are free apps).