Checkout Daten als JSON

Hallo Forengemeinde,

ich versuche gerade die Daten aus dem Checkout (am Beispiel des Paypal Gateways) als JSON zu bekommen aber sobald ich den Array in ein json_encode() packe kommt an der Ziel URL nichts an.

Hier (exemplarisch) Auszug aus dem class-wc-gateway-paypal-request.php (ab Zeile 64):

return apply_filters( 'woocommerce_paypal_args', array_merge(
			array(
				'cmd'           => '_cart',
				'business'      => $this->gateway->get_option( 'email' ),
				'no_note'       => 1,
				'currency_code' => get_woocommerce_currency(),
				'charset'       => 'utf-8',
				'rm'            => is_ssl() ? 2 : 1,
				'upload'        => 1,
				'return'        => esc_url( add_query_arg( 'utm_nooverride', '1', $this->gateway->get_return_url( $order ) ) ),
				'cancel_return' => esc_url( $order->get_cancel_order_url() ),
				'page_style'    => $this->gateway->get_option( 'page_style' ),
				'paymentaction' => $this->gateway->get_option( 'paymentaction' ),
				'bn'            => 'WooThemes_Cart',
				'invoice'       => $this->gateway->get_option( 'invoice_prefix' ) . $order->get_order_number(),
				'custom'        => json_encode( array( 'order_id' => $order->id, 'order_key' => $order->order_key ) ),
				'notify_url'    => $this->notify_url,
				'first_name'    => $order->billing_first_name,
				'last_name'     => $order->billing_last_name,
				'company'       => $order->billing_company,
				'address1'      => $order->billing_address_1,
				'address2'      => $order->billing_address_2,
				'city'          => $order->billing_city,
				'state'         => $this->get_paypal_state( $order->billing_country, $order->billing_state ),
				'zip'           => $order->billing_postcode,
				'country'       => $order->billing_country,
				'email'         => $order->billing_email
			),
			$this->get_phone_number_args( $order ),
			$this->get_shipping_args( $order ),
			$this->get_line_item_args( $order )
		), $order );

Will ich dann ersetzen durch etwa so (nur mehr Felder am Ende):

return apply_filters( 'woocommerce_paypal_args',json_encode( array( 'feld1' => $feld1, 'feld2' => $feld2 )))

Nun ja, bislang kommt da am Ende nichts an. Was ist falsch?