diff --git a/server/api/admin/board-channels.post.js b/server/api/admin/board-channels.post.js
index b49d81f..bc4a9f8 100644
--- a/server/api/admin/board-channels.post.js
+++ b/server/api/admin/board-channels.post.js
@@ -25,7 +25,9 @@ export default defineEventHandler(async (event) => {
 
   if (!slackChannelId) {
     if (process.env.ALLOW_DEV_TEST_ENDPOINTS === 'true') {
-      slackChannelId = `dev-stub-${Date.now()}`
+      // Match the Slack channel ID format (^[A-Z0-9]+$) so the value
+      // round-trips through boardChannelUpdateSchema on subsequent edits.
+      slackChannelId = `CDEV${Date.now().toString(36).toUpperCase()}`
       console.log('[slack] DEV MODE — skipping createChannel', { name: body.name, slackChannelId })
     } else {
       const slack = getSlackAdminService()