await Glassfy.initialize("8NOV6FQBHHRJ4F9N2HV0HUXOQ5LL0QA3");
var offerings = await Glassfy.offerings();
var offering = offerings.all
  ?.singleWhere((offering) => offering.offeringId == "my_offering");
var sku = offering?.skus?.first;
if (sku != null) {
var transaction = await Glassfy.purchaseSku(sku);
var permission = transaction.permissions?.all
    ?.singleWhere((permission) => permission.permissionId== "premium");
if (permission?.isValid==true) {
  // unlock premium
}