Apple server to server testing in sandbox [closed]

We are developing App in React Native which requires In-App Purchase. When the user login the first-time user has to subscribe to one of the plans. After selecting the plan we verify receipt in the backend. As we are using the sandbox for testing after selecting 1 Month plan we get 5 mins of subscription. After going into Settings->App Store->Sandbox Account and from there we are upgrading or downgrading plans but on click of plan popup comes and clicking on the purchase button plan is not changing and also server to server notifications is not coming. Also, Apple has mentioned that your server must be configured with ATS. Our server passed the ATS configuration. we have also added Server-to-Server URL to app store connect.