fix(connector): [Airwallex] Fix refunds (#1468)

Co-authored-by: SamraatBansal <samraatbansal7@gmail.com>

crates/router/src/connector/airwallex/transformers.rs

@@ -427,6 +427,7 @@ impl<F> TryFrom<&types::RefundsRouterData<F>> for AirwallexRefundRequest {
 // Type definition for Refund Response
 #[allow(dead_code)]
 #[derive(Debug, Serialize, Default, Deserialize, Clone)]
+#[serde(rename_all = "SCREAMING_SNAKE_CASE")]
 pub enum RefundStatus {
     Succeeded,
     Failed,
@@ -448,7 +449,7 @@ impl From<RefundStatus> for enums::RefundStatus {
 #[derive(Default, Debug, Clone, Serialize, Deserialize)]
 pub struct RefundResponse {
     //A unique number that tags a credit or debit card transaction when it goes from the merchant's bank through to the cardholder's bank.
-    acquirer_reference_number: String,
+    acquirer_reference_number: Option<String>,
     amount: f32,
     //Unique identifier for the Refund
     id: String,