In app purchase 2 plugin ionic 3 for ios - ios

Question

I am very beginner in developing ionic apps and trying to integrate in-app-purchase2 plugin in ionic 3 for ios. Everytime my code stop and gives error this.store.when(productId).approved( (product: IAPProduct) => {}) is not a function.
This is my try that i do till now:
configurePurchasing() {
let productId;
try {
if (this.platform.is('ios')) {
productId = this.product.appleProductId;
} else if (this.platform.is('android')) {
productId = this.product.googleProductId;
}
// Register Product
// Set Debug High
this.store.verbosity = this.store.DEBUG;
// Register the product with the store
this.store.register({
id: productId,
alias: productId,
type: this.store.CONSUMABLE
});
this.registerHandlers(productId);
this.store.ready().then((status) => {
console.log(JSON.stringify(this.store.get(productId)));
console.warn('Store is Ready: ' + JSON.stringify(status));
console.warn('Products: ' + JSON.stringify(this.store.products));
});
// Errors On The Specific Product
this.store.when(productId).error( (error) => {
alert('An Error Occured' + JSON.stringify(error));
});
// Refresh Always
console.log('Refresh Store');
this.store.refresh();
} catch (err) {
console.warn('Error On Store Issues' + JSON.stringify(err));
}
}
registerHandlers(productId) {
// Handlers
this.store.when(productId).approved( (product: IAPProduct) => {
// Purchase was approved
product.finish();
});
this.store.when(productId).registered( (product: IAPProduct) => {
console.warn('Registered: ' + JSON.stringify(product));
});
this.store.when(productId).updated( (product: IAPProduct) => {
console.warn('Loaded' + JSON.stringify(product));
});
this.store.when(productId).cancelled( (product) => {
alert('Purchase was Cancelled');
});
// Overall Store Error
this.store.error( (err) => {
alert('Store Error ' + JSON.stringify(err));
});
}
async purchase() {
let productId;
if (this.platform.is('ios')) {
productId = this.product.appleProductId;
} else if (this.platform.is('android')) {
productId = this.product.googleProductId;
}
console.log('Products: ' + JSON.stringify(this.store.products));
console.log('Ordering From Store: ' + productId);
try {
let product = this.store.get(productId);
alert('Product Info: ' + JSON.stringify(product));
// let order = await this.store.order(productId);
// alert('Finished Purchase');
} catch (err) {
console.log('Error Ordering ' + JSON.stringify(err));
}
}
From last 8 hours i am stuck at this point. Anyone here help me out in integrating this plugin. If you have any good tutorial related to this please post in comments. Thanks in advance.