Fix · Payments

Payment webhook says invalid signature

Blocks your workNot checked against the vendor's current screens

What you may see

My webhook route rejects the gateway's calls

Most likely cause

The signature is computed from the exact raw body and a shared secret; a changed body (parsed or reformatted) or the wrong secret breaks it.

Check first (about two minutes)

Check you are using the secret of the right mode (test or live) for this webhook.

The fix prompt

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The exact error or what you see

What you did before it happened

Kept only in this browser, on this device. Keys and passwords are removed before anything is saved.

Prompt language

You are a very careful senior engineer who knows online payments (including payment gateways used in Kuwait) and explains them to people who are not developers. I am not a developer, so explain every step in plain words and tell me exactly which button, menu or command you mean. If you are not sure about something, say so; do not guess.

Menu and button names change over time. If you cannot find a button or page I mention, say so and tell me what to look for instead of guessing.

THE PROBLEM
Payment webhook says invalid signature

THE EXACT ERROR OR WHAT I SEE
[paste the exact error here]

WHAT I DID BEFORE IT HAPPENED
[write in a few words what you did before it happened]

MOST LIKELY CAUSE
The signature is computed from the exact raw body and a shared secret; a changed body (parsed or reformatted) or the wrong secret breaks it.

DO THESE STEPS, IN THIS ORDER
1. Read how the gateway documents its signature (which header, which algorithm, which text is signed). Do not guess.
2. Verify using the raw body before any JSON parsing, comparing in constant time.
3. Check the webhook secret variable is the right one and has no stray spaces.
Stop and tell me if what you see does not match a step. Do not skip ahead.

CHECK THAT IT WORKED
- A signed test event passes and an unsigned one is rejected.
Tell me exactly what I should see on the screen when it works.

DO NOT CHANGE
- Do not disable the signature check.
- Anything I did not ask about: the design, the text, other pages, other settings or the data.
- Do not delete files, data or branches, do not reset or force-push, and do not rewrite history, unless you first show me exactly what would be lost and I say yes.
- Do not paste, print or ask me to paste a password or secret key into this chat. If one is needed, tell me which settings page of the right service to store it in.

WHEN YOU FINISH
Explain in simple words what you changed (file by file or setting by setting), why you changed it, and how I can undo it.

Paste it into Claude, ChatGPT, Gemini or Cursor, then follow what it says.

After you tried it, did it work?

Steps

Read how the gateway documents its signature (which header, which algorithm, which text is signed). Do not guess.
Verify using the raw body before any JSON parsing, comparing in constant time.
Check the webhook secret variable is the right one and has no stray spaces.

Do not do this

Do not log the secret or the full signature header.
Do not disable the signature check.

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