NMI Webhooks

When to Use This Skill

• How do I receive NMI (Network Merchants) webhooks?
• How do I verify the NMI Webhook-Signature header?
• Why is my NMI webhook signature verification failing?
• How do I handle transaction.sale.success, transaction.auth.success, transaction.refund.success, or transaction.void.success events?
• What is the t= value in the NMI signature header — is it a timestamp?

How NMI Webhooks Work (Read This First)

NMI does not use the Standard Webhooks spec. Each delivery carries a single custom header:

Webhook-Signature: t=f3c1e9a2b7d84c15,s=9b7c...e10a