From d43589a0f5b8b2fe935a6ad4c8e318cf5c985dd2 Mon Sep 17 00:00:00 2001
From: Dominik Ferber <dominik.ferber@gmail.com>
Date: Thu, 6 Nov 2025 14:45:49 +0200
Subject: [PATCH] @flags-sdk/growthbook: support stringified json (#210)

closes #209
---
 .changeset/ninety-starfishes-fold.md     |  5 +++++
 packages/adapter-growthbook/src/index.ts | 18 +++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/ninety-starfishes-fold.md

diff --git a/.changeset/ninety-starfishes-fold.md b/.changeset/ninety-starfishes-fold.md
new file mode 100644
index 00000000..f358904f
--- /dev/null
+++ b/.changeset/ninety-starfishes-fold.md
@@ -0,0 +1,5 @@
+---
+"@flags-sdk/growthbook": patch
+---
+
+support strings in Edge Config
diff --git a/packages/adapter-growthbook/src/index.ts b/packages/adapter-growthbook/src/index.ts
index 0fc99280..9819c0d2 100644
--- a/packages/adapter-growthbook/src/index.ts
+++ b/packages/adapter-growthbook/src/index.ts
@@ -75,7 +75,7 @@ export function createGrowthbookAdapter(options: {
   let _initializePromise: Promise<void> | undefined;
 
   const initializeGrowthBook = async (): Promise<void> => {
-    let payload: FeatureApiResponse | undefined;
+    let payload: FeatureApiResponse | string | undefined;
     if (options.edgeConfig) {
       try {
         const edgeConfigClient = createClient(
@@ -92,6 +92,22 @@ export function createGrowthbookAdapter(options: {
       }
     }
 
+    // Older GrowthBook integrations use WebHooks directly to store
+    // data in Edge Config, but they store the data as a string.
+    //
+    // We need to parse the string to JSON before passing it to GrowthBook.
+    //
+    // https://docs.growthbook.io/app/webhooks/sdk-webhooks#vercel-edge-config
+    // https://github.com/vercel/flags/issues/209
+    if (typeof payload === 'string') {
+      try {
+        payload = JSON.parse(payload) as FeatureApiResponse;
+      } catch {
+        console.error('Invalid payload format');
+        payload = undefined;
+      }
+    }
+
     await growthbook.init({
       streaming: false,
       payload,