diff --git a/src/api/viewService.ts b/src/api/viewService.ts
index 19595f2..c1c1e69 100644
--- a/src/api/viewService.ts
+++ b/src/api/viewService.ts
@@ -257,10 +257,13 @@ export function getFormScreen(
   instanceId?: string,
   deviceType = "desktop",
 ): Promise<FormScreenResponse> {
+  const numericInstanceId = instanceId ? Number(instanceId) : undefined;
   return request("POST", `/app/${APP_ID}/view/form-screens`, {
     activity_id: activityId,
     device_type: deviceType,
-    ...(instanceId ? { instance_id: instanceId } : {}),
+    ...(numericInstanceId && !Number.isNaN(numericInstanceId)
+      ? { instance_id: numericInstanceId }
+      : {}),
   });
 }