Add to calendar is a pro feature

PLAYSTORE.txt

@@ -72,6 +72,7 @@ All pro features are convenience or advanced features.
 * Synchronization scheduling
 * Reply templates
 * Accept/decline calendar invitations
+* Add message to calendar
 * Filter rules
 * Search indexing, search on server
 * Keyword management

README.md

@@ -91,6 +91,7 @@ All pro features are convenience or advanced features.
 * Synchronization scheduling ([instructions](https://github.com/M66B/FairEmail/blob/master/FAQ.md#user-content-faq78))
 * Reply templates
 * Accept/decline calendar invitations
+* Add message to calendar
 * Filter rules ([instructions](https://github.com/M66B/FairEmail/blob/master/FAQ.md#user-content-faq71))
 * Search indexing, search on server ([instructions](https://github.com/M66B/FairEmail/blob/master/FAQ.md#user-content-faq13))
 * Keyword management

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

@@ -3709,7 +3709,10 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                             onMenuShare(message, false);
                             return true;
                         case R.id.menu_event:
-                            onMenuShare(message, true);
+                            if (ActivityBilling.isPro(context))
+                                onMenuShare(message, true);
+                            else
+                                context.startActivity(new Intent(context, ActivityBilling.class));
                             return true;
                         case R.id.menu_print:
                             onMenuPrint(message);

metadata/en-US/full_description.txt

@@ -72,6 +72,7 @@ All pro features are convenience or advanced features.
 * Synchronization scheduling
 * Reply templates
 * Accept/decline calendar invitations
+* Add message to calendar
 * Filter rules
 * Search indexing, search on server
 * Keyword management