wpcf7mailsent event not working

Hi,
I have implemented a datalayer code via “wpcf7mailsent” event Listerner, but was unable to receive any response using the code.
I tried placing this code on
themes->functions.php
themes->header.php
themes->footer.php

Is there any other specific procedure to be followed for getting it worked or any other means to get the tag event fired after a successful form submit.