Fix execution model

src/models.ts

@@ -2386,7 +2386,7 @@ export namespace Models {
         /**
          * HTTP response body. This will return empty unless execution is created as synchronous.
          */
-        responseBody: payload;
+        responseBody: string;
         /**
          * HTTP response headers as a key-value object. This will return only whitelisted headers. All headers are returned if execution is created as synchronous.
          */