Added IAB

app/src/main/java/eu/faircode/email/Helper.java

@@ -31,6 +31,7 @@ import android.widget.EditText;
 import android.widget.ImageView;
 import android.widget.Spinner;
 
+import com.android.billingclient.api.BillingClient;
 import com.google.android.material.bottomnavigation.BottomNavigationView;
 
 import java.io.BufferedReader;
@@ -188,4 +189,55 @@ public class Helper {
             sb.append(String.format("%02x", b));
         return sb.toString();
     }
+
+    static String getBillingResponseText(@BillingClient.BillingResponse int responseCode) {
+        switch (responseCode) {
+            case BillingClient.BillingResponse.BILLING_UNAVAILABLE:
+                // Billing API version is not supported for the type requested
+                return "BILLING_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.DEVELOPER_ERROR:
+                // Invalid arguments provided to the API.
+                return "DEVELOPER_ERROR";
+
+            case BillingClient.BillingResponse.ERROR:
+                // Fatal error during the API action
+                return "ERROR";
+
+            case BillingClient.BillingResponse.FEATURE_NOT_SUPPORTED:
+                // Requested feature is not supported by Play Store on the current device.
+                return "FEATURE_NOT_SUPPORTED";
+
+            case BillingClient.BillingResponse.ITEM_ALREADY_OWNED:
+                // Failure to purchase since item is already owned
+                return "ITEM_ALREADY_OWNED";
+
+            case BillingClient.BillingResponse.ITEM_NOT_OWNED:
+                // Failure to consume since item is not owned
+                return "ITEM_NOT_OWNED";
+
+            case BillingClient.BillingResponse.ITEM_UNAVAILABLE:
+                // Requested product is not available for purchase
+                return "ITEM_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.OK:
+                // Success
+                return "OK";
+
+            case BillingClient.BillingResponse.SERVICE_DISCONNECTED:
+                // Play Store service is not connected now - potentially transient state.
+                return "SERVICE_DISCONNECTED";
+
+            case BillingClient.BillingResponse.SERVICE_UNAVAILABLE:
+                // Network connection is down
+                return "SERVICE_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.USER_CANCELED:
+                // User pressed back or canceled a dialog
+                return "USER_CANCELED";
+
+            default:
+                return Integer.toString(responseCode);
+        }
+    }
 }