diff --git a/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinkSettingsController.kt b/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinkSettingsController.kt
index 8e931bd..12ea025 100644
--- a/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinkSettingsController.kt
+++ b/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinkSettingsController.kt
@@ -76,10 +76,20 @@ class PayuPaymentLinkSettingsController(
             )
         } else {
             existing.merchantId = merchantId
+            val oldClientId = existing.clientId
+            val oldClientSecret = existing.clientSecret
+            val oldIsTest = existing.isTest
             if (request.clientId != null) existing.clientId = request.clientId.trim().ifBlank { null }
             if (request.clientSecret != null) existing.clientSecret = request.clientSecret.trim().ifBlank { null }
             if (request.accessToken != null) existing.accessToken = request.accessToken.trim().ifBlank { null }
             existing.isTest = isTest
+            val credsChanged = (request.clientId != null && existing.clientId != oldClientId) ||
+                (request.clientSecret != null && existing.clientSecret != oldClientSecret) ||
+                oldIsTest != isTest
+            if (credsChanged) {
+                existing.accessToken = null
+                existing.tokenExpiresAt = null
+            }
             existing.updatedAt = OffsetDateTime.now()
             existing
         }
diff --git a/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinksController.kt b/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinksController.kt
index 143531b..4960fb4 100644
--- a/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinksController.kt
+++ b/src/main/kotlin/com/android/trisolarisserver/controller/PayuPaymentLinksController.kt
@@ -125,6 +125,7 @@ class PayuPaymentLinksController(
             contentType = MediaType.APPLICATION_JSON
             set("Authorization", "Bearer $accessToken")
             set("merchantId", settings.merchantId)
+            set("mid", settings.merchantId)
         }
         val entity = HttpEntity(body, headers)
         val response = restTemplate.postForEntity(resolveBaseUrl(settings.isTest), entity, String::class.java)