diff --git a/packages/platform-server/src/transfer_state.ts b/packages/platform-server/src/transfer_state.ts
index 26e8b3fed67a23..8796b02e787780 100644
--- a/packages/platform-server/src/transfer_state.ts
+++ b/packages/platform-server/src/transfer_state.ts
@@ -21,15 +21,20 @@ export const TRANSFER_STATE_SERIALIZATION_PROVIDERS: Provider[] = [{
function serializeTransferStateFactory(doc: Document, appId: string, transferStore: TransferState) {
return () => {
+ // The `.toJSON` here causes the `onSerialize` callbacks to be called.
+ // These callbacks can be used to provide the value for a given key.
+ const content = transferStore.toJson();
+
if (transferStore.isEmpty) {
// The state is empty, nothing to transfer,
// avoid creating an extra `