"Θα σε προσκαλέσω στον γάμο μου." is one of the accepted translations. So, if your sentence was not accepted it was not due to "στον". It would have helped if you had made a Report:
Here's how to report.
Go to the bottom of the exercise page where you'll see REPORT Click on that:
Then choose what you want to REPORT: (You'll see these to choose from.)
-The audio does not sound correct.
-The dictionary hints on hover are wrong or missing.
-The Greek sentence is unnatural or has an error.
-The "Correct solution" is unnatural or has an error.
-My answer should be accepted. This is the one you should click on if your translation was not accepted