diff --git a/src/routes/qbo.js b/src/routes/qbo.js
index 2a1e1f1..a41fa5e 100644
--- a/src/routes/qbo.js
+++ b/src/routes/qbo.js
@@ -337,7 +337,7 @@ router.post('/record-payment', async (req, res) => {
             CustomerRef: { value: custIds[0] },
             TotalAmt: totalAmt,
             TxnDate: payment_date,
-            PaymentRefNum: reference_number || '',
+            PaymentRefNum: (reference_number || '').substring(0, 21) || undefined,
             PaymentMethodRef: { value: payment_method_id },
             DepositToAccountRef: { value: deposit_to_account_id },
             Line: invoicesData.map(inv => ({