diff --git a/signal-server-openapi.yaml b/signal-server-openapi.yaml
index 3ea296581..9fc3bb181 100644
--- a/signal-server-openapi.yaml
+++ b/signal-server-openapi.yaml
@@ -3073,6 +3073,10 @@ paths:
 
         After calling this method, the payment is confirmed. Callers must durably store their subscriberId before calling
         this method to ensure their payment is tracked.
+
+        Once a purchaseToken to is posted to a subscriberId, the same subscriberId must not be used with another payment
+        method. A different playbilling purchaseToken can be posted to the same subscriberId, in this case the subscription
+        associated with the old purchaseToken will be cancelled.
       operationId: setPlayStoreSubscription
       parameters:
       - name: subscriberId