Getting User Entered Form Data within a hook function
You can user this code in which you can add your form data in array and pass it to the Paypal api.

function do_custom_commerce_paypal_api_request_alter(&amp;$nvp, $order, $payment_method){
    if ($payment_method['base'] == 'commerce_paypal_wpp' ) { //check payment method

        //save form data
        $name = $form_state['values']['field_name'];
        $organization = $form_state['values']['field_organization'];

        $nvp += array(
        'name' =&gt; $name,
        'organization' =&gt; $organization,
    );
  }
}


Here is the similar solution for your problem in which user has passed order details. Click Here