src/Payum/Core/Gateway.php
public function addApi($api, $forcePrepend = false)
    {
        $forcePrepend ?
            array_unshift($this->apis, $api) :
            array_push($this->apis, $api)
        ;
    }
public function addApi($api, $forcePrepend = false)
    {
        $forcePrepend ?
            array_unshift($this->apis, $api) :
            array_push($this->apis, $api)
        ;
    }
@param mixed $api
@param bool  $forcePrepend

@return void