rpress_get_payment_subtotal

This filter is applied to use the payment subtotal amount data of orders, it is including two parameters.
$this->subtotal is got the subtotal value.
$this->ID is used to get id.

An example of how you can append additional information:

function get_subtotal( $subtotal ){
// return subtotal value;
return $subtotal;
}
add_filter( 'rpress_get_payment_subtotal', 'get_subtotal',10, 2 );