Clone and run npm install, If you wish to update to the latest Ionic delete the node_modules and run below,
ng update @angular/core @angular/cli npm install @ionic/angular-toolkit@latest ionic cordova plugin add cordova-plugin-stripe npm install --save @ionic-native/stripe npm WARN @ionic-native/stripe@5.31.1 requires a peer of @ionic-native/core@^5.1.0 but none is installed. You must install peer dependencies yourself. You need to install manually as below
npm i @ionic-native/core Make sure your Ionic project is integrated with Capacitor and not Cordova
npm install cordova-plugin-stripe npm install @ionic-native/stripe ionic cap sync /src/payments/payments.page.ts
this.stripe.setPublishableKey('pk_test_xxxxxxxxxxx'); 