Is it possible to POST values to another page from the FORM SUBMIT function I have a module that allows authenticated users to book a "Facility" and then pay for it online. The module that facilitates the online payment is different from the booking module.

In the booking module I accept the details from the "authenticated" user in a form and in submit function I store the record in the DB with the following code

$form['$source'] = array(
  '#type' =&gt; 'hidden',
  '#default_value' =&gt; 'obb',
);

$form['uv_amount'] = array(
  '#type' =&gt; 'hidden',
  '#default_value' =&gt; $amount_final,
);

$form['description1'] = array(
  '#type' =&gt; 'hidden',
  '#default_value' =&gt; 'OBB - Booking Charges for ' . $hall_type_code . ' ON ' . $arri_date,
);

$form['#method'] = 'post';
$form['#action'] = '/mymodule/pgi/confirm';


In the module that handles the payment gateway I pass these values to the payment gateway after calculating the mandatory HASH values etc (as per the payment gateway integration document)

During testing I figured out that the values are not being posted to the PG page. Is there a way to post the values to the PG page after I store the booking/reservation details in the form submit function? Or is there a better way of accomplishing this. Would appreciate any help.
It sounds like you are doing a multi step form (given the URL in your form is "confirm"). You don't want to be looking at $_POST values, you'll want to utilize FormAPI all the way through.

See for examples:

http://www.sitepoint.com/building-multi-page-wizard-like-form-drupal/

http://jamesdavidson.io/blog/how-create-multi-step-form-drupal-7

http://www.webomelette.com/ctools-object-cache-multi-step-form