src/Payum/Paypal/ExpressCheckout/Nvp/Api.php
public function setExpressCheckout(array $fields)
    {
        if (false == isset($fields['RETURNURL'])) {
            if (false == $this->options['return_url']) {
                throw new RuntimeException('The return_url must be set either to FormRequest or to options.');
            }

            $fields['RETURNURL'] = $this->options['return_url'];
        }

        if (false == isset($fields['CANCELURL'])) {
            if (false == $this->options['cancel_url']) {
                throw new RuntimeException('The cancel_url must be set either to FormRequest or to options.');
            }

            $fields['CANCELURL'] = $this->options['cancel_url'];
        }

        $fields['METHOD'] = 'SetExpressCheckout';

        $this->addVersionField($fields);
        $this->addAuthorizeFields($fields);

        return $this->doRequest($fields);
    }
public function setExpressCheckout(array $fields)
    {
        if (false == isset($fields['RETURNURL'])) {
            if (false == $this->options['return_url']) {
                throw new RuntimeException('The return_url must be set either to FormRequest or to options.');
            }

            $fields['RETURNURL'] = $this->options['return_url'];
        }

        if (false == isset($fields['CANCELURL'])) {
            if (false == $this->options['cancel_url']) {
                throw new RuntimeException('The cancel_url must be set either to FormRequest or to options.');
            }

            $fields['CANCELURL'] = $this->options['cancel_url'];
        }

        $fields['METHOD'] = 'SetExpressCheckout';

        $this->addVersionField($fields);
        $this->addAuthorizeFields($fields);

        return $this->doRequest($fields);
    }
Require: PAYMENTREQUEST_0_AMT

@param array $fields

@return array