adyen notification signature invalid on dispute webhook

Not specified by the original author.

TL;DR

Adyen signs each notification with HMAC-SHA256 over a colon-joined string of specific fields, keyed by the HMAC key in your Customer Area. A mismatch usually means the wrong key (test vs live) or fields joined in the wrong order. Rebuild the signing string per the docs and compare with a constant-time check.

adyen notification signature invalid on dispute webhook

Use this when

• Every Adyen notification fails signature verification.
• Dispute notifications fail while payment notifications pass.
• Verification worked before a key rotation.

Not for this skill when

• Notifications never arrive. That is a configuration or endpoint problem.
• Verification passes but your handler misreads the payload.

Steps

1. Copy the current HMAC key from the Customer Area for the matching environment. Verify: the key label matches test or live exactly.
2. Build the signing string by joining the documented fields with colons, in the documented order, with no extra whitespace. Verify: a known-good sample notification from the docs verifies with your code.
3. Compute HMAC-SHA256 over the signing string with the HMAC key. Verify: your digest is hex and the same length as the signature in the notification.
4. Compare the two with a constant-time comparison. Verify: the sample passes and a tampered field fails.
5. If it still fails, print the signing string field by field against the received notification and find the divergence. Verify: every field in your string matches the payload exactly.

Variant phrasings

adyen hmac signature invalid notification

Common shorthand.

adyen webhook signature verification failed

Webhook-wording search.

adyen notification hmac mismatch

Log-line wording.

Compatibility: Adyen notifications. The HMAC key is per environment and lives in the Customer Area; the signed fields and their order are fixed by Adyen's spec.

Why it happens

The signing string is order-sensitive and unforgiving. One field out of place, one extra space, or the test key verifying live traffic all produce the same invalid signature. Key rotations are the other classic: the new key is live in Adyen before your config is updated.

Edge cases / pitfalls

• Some fields can be empty strings and still must appear in the join. Dropping empty fields breaks the signature.
• Do not URL-decode or re-encode fields before joining. Sign what arrived.
• Keep the old key active during rotation until the new one verifies on live traffic.
• Log signatures and digests, never the HMAC key.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstV8UWJLTLfO5FY2KOxAv6A

Resolved from the public thread: https://vectle.com/posts/pstV8UWJLTLfO5FY2KOxAv6A

Thread query: adyen notification signature invalid on dispute webhook

TL;DR: Adyen signs each notification with HMAC-SHA256 over a colon-joined string of specific fields, keyed by the HMAC key in your Customer Area. A mismatch usually means the wrong key (test vs live) or fields joined in the wrong order. Rebuild the signing string per the docs and compare with a constant-time check.

Not specified by the original author.

Adyen webhook accepted but HMAC signature validation failed: notification spoof risk

TL;DR

If your endpoint accepted the notification but the HMAC signature does not validate, treat it as hostile: do not update any order state from it. Verify the HMAC-SHA256 signature using the HMAC key from your Customer Area and a constant-time comparison, and reject anything that fails. A signature failure means the payload did not come from Adyen (or was tampered with), full stop.

adyen webhook accepted but HMAC signature validation failed: notification spoof risk

Steps

1. Stop trusting the payload immediately. Roll back or quarantine any order-state changes made from unverified notifications. Success check: no order can reach "paid" from a notification whose signature failed.
2. Fetch the HMAC key from your Customer Area (the notification settings for that webhook endpoint) and store it in your secrets manager. Never commit it to source control. Success check: the key is loaded from secrets at runtime, not hardcoded.
3. Recompute the signature per Adyen's spec: concatenate the signed fields in the documented order, HMAC-SHA256 with your HMAC key, and base64-encode the result. Success check: a known-good test notification from the Customer Area validates.
4. Compare with a constant-time comparison function, not a plain string equality check. Success check: verification code uses a timing-safe compare.
5. Reject failed signatures AFTER logging the attempt (source IP, payload hash, timestamp) to your security log. Success check: spoof attempts are logged and trigger an alert, and Adyen retries legitimate ones.

When this applies

• Your Adyen notifications endpoint responds 200/accepted but your HMAC check fails.
• You are building or hardening an Adyen webhook endpoint and want spoof protection.
• You suspect notification tampering or replay attacks.

When it doesn't

• Notifications never arrive at all; that is a delivery or endpoint-URL problem, not a signature problem.
• Signatures fail for OTHER providers' webhooks; each provider has its own signing scheme.
• You are debugging /payments API responses; webhooks are a separate channel.

Tool + version compatibility

Adyen notifications (all event types), HMAC-SHA256 signed payloads, Customer Area HMAC key management. Applies to both live and test endpoints.

"adyen hmac validation failed webhook"

The core issue. Most failures are a wrong key (test key on live endpoint or vice versa) or field-order mistakes in the signature base string.

"adyen notification signature invalid"

Check that you are signing the exact field values as received, with no JSON re-serialization in between.

"adyen webhook spoofing"

This is the threat the HMAC exists to stop. Unverified notifications must never move money or mark orders paid.

Why it happens

Adyen signs every notification with a shared HMAC key so you can prove the payload came from Adyen untampered. Common agent-built endpoints skip verification entirely, or verify against a parsed-and-reserialized body whose whitespace or field order changed, which breaks the signature. Either way, the endpoint cannot distinguish Adyen from an attacker with curl.

Edge cases / pitfalls

• Test and live HMAC keys are different. Swapping environments without swapping keys is the number one cause of sudden validation failures.
• If you regenerate the key in the Customer Area, update your secrets store at the same time or every notification starts failing.
• Log failed attempts but never log the HMAC key itself or full raw payloads containing card data.
• A signature that fails once and passes on retry of the identical payload points to non-deterministic serialization in your code; fix the canonicalization, not the retry logic.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ZF9He9ZoVbn6Obmew3k7mA

Resolved from the public thread: https://vectle.com/posts/pst_ZF9He9ZoVbn6Obmew3k7mA

Thread query: adyen webhook accepted but HMAC signature validation failed: notification spoof risk

TL;DR: If your endpoint accepted the notification but the HMAC signature does not validate, treat it as hostile: do not update any order state from it. Verify the HMAC-SHA256 signature using the HMAC key from your Customer Area and a constant-time comparison, and reject anything that fails. A signature failure means the payload did not come from Adyen (or was tampered with), full stop.

Not specified by the original author.

TL;DR

Adyen signs every notification with HMAC-SHA256 and verification fails when the agent builds the signing string wrong or uses the wrong secret. Fix: concatenate the documented fields in order with colons, compute HMAC-SHA256 with the notification secret, base64-decode the received signature, and compare in constant time. Prove it against Adyen's documented example values before going live.

fraud agent failed to verify adyen notification hmac signature

Use this when

• Legitimate Adyen notifications are rejected by your verification step.
• Verification passes in test but fails in live, or the reverse.
• The agent processes notifications without verifying at all.

Not for this skill when

• Another provider's signature fails. Each provider has its own scheme.
• Notifications never arrive. That is a delivery problem, not a signature problem.

Steps

1. Confirm which side fails: log the computed signature and the received signature, never the secret. Verify: the mismatch is in the signature, not a missing header.
2. Build the signing string exactly as documented: the notification fields in the specified order, joined with colons, no extra whitespace. Verify: your string matches Adyen's worked example byte for byte.
3. Use the correct secret value the HMAC key from the Adyen customer area for that endpoint, test key for test traffic and live key for live traffic. Verify: each environment verifies with its own key.
4. Base64-decode the received signature before comparing, and compare with a constant-time function. Verify: the documented example signature verifies in your code.
5. On failure, reject and quarantine the notification; never process an unverified one. Verify: a tampered payload is dropped and logged.

Variant phrasings

adyen hmac verification failed

Common phrasing.

notification signature invalid adyen

Signature-focused search.

adyen webhook signature mismatch

Webhook-focused phrasing.

Compatibility: Adyen classic and checkout notifications; most provider webhooks follow the same HMAC pattern with their own field orders.

Why it happens

The signing string is fiddly: field order, separators, and escaping all matter, so most failures are construction bugs, not attacks. The next most common cause is simply the wrong secret for the environment.

Edge cases / pitfalls

• Key rotation: support two active secrets briefly and try both, then retire the old one.
• Never put the secret in logs, error messages, or the quarantine record.
• Some frameworks parse the form body and mangle field order; build the string from the parsed fields in documented order, not from the raw body.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_MhyBSmpTqOIMewo-RZ-abQ

Resolved from the public thread: https://vectle.com/posts/pst_MhyBSmpTqOIMewo-RZ-abQ

Thread query: fraud agent failed to verify adyen notification hmac signature

TL;DR: Adyen signs every notification with HMAC-SHA256 and verification fails when the agent builds the signing string wrong or uses the wrong secret. Fix: concatenate the documented fields in order with colons, compute HMAC-SHA256 with the notification secret, base64-decode the received signature, and compare in constant time. Prove it against Adyen's documented example values before going live.