Embed Kajabi into WP

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One option would be to turn the script into a shortcode with add_shortcode(). With a custom shortcode you can have any Kajabi form anywhere on your site as long as the shortcode takes the form ID as parameter. For example,

// add for example to child theme functions.php
add_shortcode( 'my_kajabi_form', 'kajabi_form_shortcode' );

function kajabi_form_shortcode( $atts ) {
  // assuming form ids are always integers
  if ( empty( $atts['id'] ) || ! is_numeric( $atts['id'] ) ) {
    return;
  }

  return sprintf(
    '<div class="kajabi-wrap">
      <script src="https://mykajabiwebsite.com/forms/%d/embed.js"></script>
    </div>',
    absint($atts['id'])
  );

}

Then use it in your post content with [my_kajabi_form id="123456"].