Si el HTML que nos pasaste es el correcto y desde Javascript no generas mas campos dinamicamente,
te estan faltando campos y por eso puden estar vacios.
Código HTML:
Ver original<input type="text" name="first_name" id="first_name" value="" size="30" maxlength="50" style="width:250px" required/> <input type="text" name="last_name" id="last_name" value="" size="30" maxlength="50" style="width:250px" required/> <input type="text" name="phone" id="phone" value="" size="30" maxlength="50" style="width:250px" required/> <input type="text" name="email" id="email" value="" size="30" maxlength="50" style="width:250px" required/> <input type="text" name="pickup_city" id="pickup_city" value="" size="30" maxlength="50" style="width:250px" /> <input type="text" name="zip_code_pickup" id="zip_code_pickup" value="" size="10" style="width:250px" /> <select name="pickup_country_id" id="pickup_country_id"></select> <select *name="pickup_state_code" id="pickup_state_code"></select>
Aca hay 7 campos y en el script php esperas 21.