How to recover the discount value of a Coupon?

Hi everyone, how are you? This is my first post :D.

I need a help if possible. I have a form that has some products and I achieved to make only one product in the list, with custom price if a certain option (radio) is checked, which is great.

However I have tried many ways but I can’t recover the final discount value applied by some coupon. I want to be able to use this coupon value to subtract from the price.

My code so far.

function changeP( $product_info, $form, $entry ) {
	if ( rgar( $entry, '143' ) == '3' ) {
		//Get the total value of the field '83' 
		$price = $product_info['products'][83]['price'];
		//If the coupon exists get the amount 
		$couponAmount = rgars( $entry, 'couponAmount' );
		$product_info = array(
			'products' => array(
					'name'     => 'All Products',
					'price'    => $price - $couponAmount,
					'quantity' => 1,
    return $product_info;
add_filter( 'gform_product_info', 'changeP', 10, 3 );

Sorry for bad English

Can someone help me?