Android in-app billing: Can’t start async operation because another async operation (is in progress)

A simple tricky solution

before calling purchaseItem method just add this line

  if (billingHelper != null) billingHelper.flagEndAsync();

so your code looks this way

 if (billingHelper != null) billingHelper.flagEndAsync();
 purchaseItem("android.test.purchased");

Note: don’t forget to make public flagEndAsync() method in IabHelper if you call it from another package.