After using wpcf7_before_send_mail in contact form 7 the wheel spins endlessly, why?

Question

WordPress

I am using the construct:

add_action( 'wpcf7_before_send_mail', 'wpcform7' );

function wpcform7( $contact_form ) {
/* испольняемый код */
}

As a result, the letter arrives in the mail. And the function code is executed. But the ajax send wheel is spinning endlessly. Is the function supposed to return something at the end?