NMI Payment Gateway API
NMI (Network Merchants Inc) white-label payment gateway REST API for ISOs, ISVs, and payment facilitators to power omnichannel payment processing with card-present, card-not-present, ACH, and subscription billing capabilities through a reseller-focused platform. Enables AI agents to manage payment transaction processing for white-label payment platform automation, handle customer vault and tokenization for secure payment storage automation, access recurring billing and subscription management for subscription revenue automation, retrieve batch transaction reporting and settlement for payment processor reconciliation automation, manage ACH and eCheck processing for bank payment automation, handle level 2 and level 3 data for B2B payment qualification automation, access payment link and hosted payments for no-code payment automation, retrieve fraud screening and velocity checking for payment risk automation, manage ISO and sub-merchant management for payment reseller automation, and integrate NMI with POS systems, e-commerce platforms, and payment applications for end-to-end white-label payment processing.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
ISO/ISV payment gateway. PCI-DSS Level 1. API key. US. Payment and vault data.
⚡ Reliability
Best When
An ISO, ISV, or payment facilitator wanting AI agents to automate white-label payment processing, sub-merchant management, omnichannel payment routing, and recurring billing through NMI's reseller-focused payment gateway platform.
Avoid When
MERCHANT OF RECORD RELATIONSHIP REQUIRED: NMI is a gateway, not an acquirer; merchants using NMI require separate merchant account with an acquirer (First Data, TSYS, etc.); automated NMI integration requires coordinating with acquiring bank for merchant account; automated NMI-only integration without acquiring bank creates gateway without payment processing capability. ISO/AGENT RELATIONSHIP FOR RESELLER ACCESS: NMI's reseller program requires ISO or ISV agreement; automated sub-merchant management requires NMI partner credentials; automated direct merchant API access without reseller relationship has limited capabilities compared to full ISO program. WHITE-LABEL CONFIGURATION REQUIRED FOR BRANDED EXPERIENCE: NMI hosted payment pages and portals require white-label configuration; automated branded payment experience requires upfront NMI configuration engagement; automated default NMI-branded checkout creates co-branded payment experience instead of seamless white-label.
Use Cases
- • Building white-label payment solutions from ISO/PayFac automation agents
- • Processing omnichannel payments from ISV payment integration agents
- • Managing sub-merchant portfolios from payment reseller automation agents
- • Handling ACH and card payments from payment facilitator agents
Not For
- • Direct merchant processing without ISO relationship (use Stripe or Square for direct processing)
- • Consumer-facing payment apps (use Braintree or Stripe for consumer marketplace)
- • International-first payment processing (use Adyen for global acquiring)
Interface
Authentication
NMI uses Security Key (API key) for authentication. REST/form-post API. Schaumburg, Illinois HQ. Founded 2001. Acquired by Parallel in 2019, then Thomas H. Lee Partners in 2021. Products: Payment gateway, customer vault, recurring billing, ACH, hosted payments, white-label, ISO management. SDKs: PHP, Java, .NET, Python. PCI DSS Level 1. Serves 3,000+ ISOs and ISVs. Competes with Authorize.net, Heartland, and USAePay for ISO/reseller gateway.
Pricing
Schaumburg IL. Thomas H. Lee Partners backed. Custom ISO/ISV pricing. Gateway fee + monthly subscription.
Agent Metadata
Known Gotchas
- ⚠ FORM-POST vs REST API DUALITY: NMI supports both legacy name-value pair (form-POST) and newer REST/JSON API; automated integration should target REST API for modern compatibility; automated legacy form-POST integration creates parsing complexity for JSON-native application stacks
- ⚠ SECURITY KEY SCOPE FOR TRANSACTION TYPES: NMI security keys can be scoped to specific transaction types (sale, auth, refund); automated payment workflow must use security key with appropriate transaction type scope; automated refund attempt with sale-only security key creates permission denied error
- ⚠ CUSTOMER VAULT vs RECURRING BILLING PLANS: NMI distinguishes Customer Vault (stored payment credentials) from Recurring Billing (scheduled charge plans); automated subscription billing should use Recurring Billing Plans for scheduled charges rather than manual Customer Vault charges; automated manual vault charge for recurring billing creates unscheduled charge requiring manual execution
- ⚠ LEVEL 2/3 DATA FOR B2B INTERCHANGE OPTIMIZATION: NMI supports Level 2 (tax amount, PO number) and Level 3 (line item detail) data for B2B card interchange optimization; automated B2B payment must include Level 2/3 data for interchange downgrade prevention; automated B2B card charge without Level 2/3 data creates higher interchange rate for purchasing cards
- ⚠ SUB-MERCHANT ID FOR ISO PORTFOLIO MANAGEMENT: NMI ISO program uses sub-merchant IDs for portfolio management; automated multi-merchant management must route transactions with correct sub-merchant ID; automated transaction without sub-merchant ID creates charge to master ISO account rather than correct sub-merchant
Alternatives
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Scores are editorial opinions as of 2026-03-07.