Capturing The IP Address of a Form Submitter

nf1-register-ip-field.php

<?php
// Register our IP collection field.
// Because our field doesn't have any backend editing options, we only need to specify a few things.
function register_ip_field() {
  $args = array(
      'name' => 'User IP', // This will be the label of the field button in the back-end editor.
      'display_function' => 'collect_user_ip_display', // This function will be called when the form is rendered on the front-end.
      'sidebar' => 'template_fields', // This is the sidebar on the Field Settings tab that this field will show up in.
      'display_label' => false, // Since we're adding a hidden form, we don't want to show the label on the front-end.
      'display_wrap' => false, // Again, this is a hidden field, so we don't need the div wrapper that's normally output to the front-end.
  );
  
  if( function_exists( 'ninja_forms_register_field' ) ) {
      ninja_forms_register_field('user_ip', $args);
  }
}

add_action( 'init', 'register_ip_field' );

nf2-output-ip-field.php

<?php
// The only thing we have left to do is create the function that will output the HTML for the field when the form is rendered.
/*
 *	This function only has to output the specific field element. The wrap is output automatically.
 *
 *	$field_id is the id of the field currently being displayed.
 *	$data is an array the possibly modified field data for the current field.
 *
*/
function collect_user_ip_display( $field_id, $data ){
    $ip = $_SERVER["REMOTE_ADDR"]; // Get our user's IP address.
    // The "name" attribute below is very important. It has to be ninja_forms_field_$field_id
    ?>
    <input type="hidden" name="ninja_forms_field_<?php echo $field_id;?>" value="<?php echo $ip;?>">
    <?php
}

nf3-complete-ip-field.php

<?php
// Register our IP collection field.
// Because our field doesn't have any backend editing options, we only need to specify a few things.
function register_ip_field() {
  $args = array(
      'name' => 'User IP', // This will be the label of the field button in the back-end editor.
      'display_function' => 'collect_user_ip_display', // This function will be called when the form is rendered on the front-end.
      'sidebar' => 'template_fields', // This is the sidebar on the Field Settings tab that this field will show up in.
      'display_label' => false, // Since we're adding a hidden form, we don't want to show the label on the front-end.
      'display_wrap' => false, // Again, this is a hidden field, so we don't need the div wrapper that's normally output to the front-end.
  );
  
  if( function_exists( 'ninja_forms_register_field' ) ) {
      ninja_forms_register_field('user_ip', $args);
  }
}

add_action( 'init', 'register_ip_field' );
/*
 *	This function only has to output the specific field element. The wrap is output automatically.
 *
 *	$field_id is the id of the field currently being displayed.
 *	$data is an array the possibly modified field data for the current field.
 *
*/
function collect_user_ip_display( $field_id, $data ){
    $ip = $_SERVER["REMOTE_ADDR"]; // Get our user's IP address.
    // The "name" attribute below is very important. It has to be ninja_forms_field_$field_id
    ?>
    <input type="hidden" name="ninja_forms_field_<?php echo $field_id;?>" value="<?php echo $ip;?>">
    <?php
}