how can I block in-app apple purchases

You can restrict the ability to make in-App purchases, install or delete Apps -musing ScreenTime restrictions:

Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > In-app Purchases

Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Installing Apps

Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps

Either property can be set to Allow or Don’t Allow; the latter will inhibit this action.

dreion240 wrote:

I add a payment on my card I don’t want it and I don’t know how to take it off

See:

Remove a payment method from your Apple ID - Apple Support

I add a payment on my card I don’t want it and I don’t know how to take it off