How can I pay the zwift services from mobile app?
Translation: you can’t (pay from the mobile app).
“For apps and in-app products offered through Google Play, the service fee is equivalent to 30% of the price. You receive 70% of the payment. The remaining 30% goes to the distribution partner and operating fees.” (google)
Translation: you save 30% paying to Zwift directly.
Not 100% correct, since app developers who decide to manage subscriptions by themselves need staff to perform some of the functions Google would do otherwise, but close enough.