Ninja form Redirect depending on text field content [closed]

I am not sure whether you have hooked this function to appropriate action. Also you have not concatenated the strings properly:

Instead of $newdestinationurl = $url/$destinationurlslug ; it should be $newdestinationurl = $url."https://wordpress.stackexchange.com/".$destinationurlslug ;

Please see below for the complete code:

function ninja_forms_handler() {
  add_action ( 'ninja_forms_post_process', 'change_ninja_forms_landing_page', 1, 2 );
}
add_action('init', 'ninja_forms_handler');

function change_ninja_forms_landing_page(){
    global $ninja_forms_processing; 

    $form_id = $ninja_forms_processing->get_form_ID(); 

        if( $form_id == 1 ){ 
        $destinationurlslug = $ninja_forms_processing->get_field_value( 1 );         
        $url = "http://www.blablabla.com";
        $newdestinationurl = $url."https://wordpress.stackexchange.com/".$destinationurlslug ;        
        /* $url now contains our new redirection page. Let's update the form setting. */
        $ninja_forms_processing->update_form_setting( 'landing_page', $newdestinationurl ); 
    }     
}

Make sure if you use this method that you do not have an actual redirect notification created or it will take precedence. So simply deactivate the “Success Message” from “Emails & Actions” tab for your form.