Flow webhook URL validation fails — endpoint returns HTTP 200 but UI shows "Invalid URL"

Hi Klaviyo Support,

We’re unable to save or edit Flow webhook (HTTP Request) actions pointing to our endpoint. The UI shows:

Invalid URL: https://brutebonen.nl/klaviyo-branddag

This happens when creating a new webhook, editing an existing one, or saving a cloned flow — any change that touches the webhook triggers re-validation and fails.

Our endpoint is working. We’ve verified from multiple clients and from our server logs:

• GET https://brutebonen.nl/klaviyo-branddag → HTTP 200
  Response: {"success":true,"endpoint":"klaviyo-token","method":"POST"}
• POST with {} (no auth) → HTTP 200
• HEAD / OPTIONS → HTTP 200
• No redirects (non-www only; www redirects to non-www)
• Valid TLS certificate

We also tested these paths — all return 2xx from our side:

• https://brutebonen.nl/wp-json/brutebonen/v1/token/klaviyo
• https://brutebonen.nl/wp-json/brutebonen/v1/token/klaviyo-branddag
• https://brutebonen.nl/klaviyo-branddag

The problem is on Klaviyo’s side. When we attempt to save the webhook in the Flow builder, no request from Klaviyo reaches our server (checked via access logs). The error appears before any HTTP call is made, or your validation service is failing without contacting our origin.

Historical note: on 12 June 2026 ~17:05 UTC we did see one validation request from AWS (54.227.183.160, User-Agent got/…) that received 404 on GET /wp-json/brutebonen/v1/token/klaviyo (before we added a GET handler). Since fixing that (all methods now return 2xx), we see zero validation attempts from Klaviyo when the UI shows "Invalid URL".

Other external webhooks to our site work fine (e.g. Mollie, Sendcloud). Klaviyo’s own integration traffic to our WooCommerce REST API (207.211.x.x, Klaviyo/1.0) also returns 200.

We need to use this webhook in a live email flow (soft-login token for customers). We cannot proceed while URL validation blocks every save — including on flows where the same URL was previously saved.

Please:

1. Investigate why your Flow webhook URL validation rejects a URL that meets your documented requirements (HTTPS, no redirect, valid cert).
2. Clear any cached “invalid” state for our domain/paths from the earlier 404.
3. Confirm whether this is related to the platform issue reported in your community (“Invalid URL” but works in Postman).

Happy to provide access log excerpts or run a live test while you monitor on your end.

Thanks,

Jop