DataLayer event is fired even when form submission is not completed

Problem:

It seems that the dataLayer event 'petitionSignup' is fired even when there's an error with the submission on Engaging Networks Form.

Obs: I don't know the possible causes of this form submission error, but in any case, the event should not be fired. 

Why is this important?

• Not reliable data (since the signup didn't actually happen)
• NROs keep daily or weekly track of their petition signup via Google Analytics data, which means that this should be accurate. If there's a problem with submissions and the conversions are not dropping, they would probably take much more time to notice the issue (for example, a problem with the API Keys of Engaging Networks). 

Desired behaviour:

The dataLayer event 'petitionSignup' should only be fired when the data is correctly sent to the Engaging Networks database. 

There should be no event fired if there's a form submission error. 

Possible solutions: 

There's a solution suggested by Luca Tiralongo to create a condition for the event based on the display of the Thank You Message or the redirection of the user to another url (thank you page).