diff --git a/modules/ppcp-api-client/src/Endpoint/PayUponInvoiceOrderEndpoint.php b/modules/ppcp-api-client/src/Endpoint/PayUponInvoiceOrderEndpoint.php
index 23a330a67..91d1ba79a 100644
--- a/modules/ppcp-api-client/src/Endpoint/PayUponInvoiceOrderEndpoint.php
+++ b/modules/ppcp-api-client/src/Endpoint/PayUponInvoiceOrderEndpoint.php
@@ -111,6 +111,7 @@ class PayUponInvoiceOrderEndpoint {
 			),
 		);
 
+		$data = $this->ensure_tax( $data );
 		$data = $this->ensure_tax_rate( $data );
 		$data = $this->ensure_shipping( $data, $payment_source->to_array() );
 
@@ -196,6 +197,27 @@ class PayUponInvoiceOrderEndpoint {
 		);
 	}
 
+	/**
+	 * Ensures items contains tax.
+	 *
+	 * @param array $data The data.
+	 * @return array
+	 */
+	private function ensure_tax( array $data ): array {
+		$items_count = count( $data['purchase_units'][0]['items'] );
+
+		for ( $i = 0; $i < $items_count; $i++ ) {
+			if ( ! isset( $data['purchase_units'][0]['items'][ $i ]['tax'] ) ) {
+				$data['purchase_units'][0]['items'][ $i ]['tax'] = array(
+					'currency_code' => 'EUR',
+					'value'         => '0.00',
+				);
+			}
+		}
+
+		return $data;
+	}
+
 	/**
 	 * Ensures items contains tax rate.
 	 *