Invalid IPN signature
/api/webhooks/nowpayments (IPN) rejected the request because the signature did not match (400 Invalid IPN signature.).
Why this happens
Wrong IPN/webhook secret in Admin Payment settings, truncated body, or a forged/replayed request. The site will not credit the payment until signatures verify.
Diagnose and fix
1. Admin → Settings → Payment → NOWPayments — paste the IPN/webhook secret exactly as shown in NOWPayments.
2. Confirm the webhook URL is the live HTTPS endpoint (no middleboxes altering the body).
3. Retry a test payment; check webhook delivery logs at the provider.
4. Distinct from business “payment failed” — this is auth of the callback itself.