Flutter Expert - Need to add Subscription page in my existing Android & ios App

I already have my app in (Android) Play Store & (ios) App Store. I need someone experienced in adding a subscription page to both of my apps. Firstly need the design idea and then we must start implementing. I will share the code in github and you must start the work. I will share you a similar app, which have the same functionality i need and you can take reference of design and functionality from that app. I am waiting for Genuine Offers. Thanks