The mobile app allows you to post products , and you should buy a package to have access to posting, (for example you are buying package which allows you to post 10 products and etc.) which payment method is allowed for that? Can I go with some third party payment for example Apple Pay + Stripe or I must use in app purchase for that?
Digital goods/services require Apple IAP. other than that if the goods are physical then you can use 3rd party payment gateways.