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Diameter is a banking infrastructure API that sits between your fintech product and partner banks, giving you a single, unified REST interface to handle the full lifecycle of end-user onboarding, virtual account management, and payment processing — without requiring a direct integration with each bank.

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What Diameter Solves

Building compliant, bank-connected financial products is slow and expensive. Every bank speaks a different protocol, enforces different onboarding rules, and surfaces payments through a different API. Diameter abstracts all of that away. You integrate once and gain access to multiple partner banks and payment rails through a consistent set of endpoints and data models.

Quickstart

Obtain credentials, create your first end user, and fire a wire payment in under 15 minutes.

Authentication

Learn how OAuth2 Client Credentials work, which scopes to request, and how to handle token expiry.

Core Concepts

Understand Tenants, Products, End Users, Accounts, and Payments before you write your first request.

API Reference

Browse every endpoint, request schema, and response model in the full OpenAPI reference.

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Key Capabilities

End-User Onboarding

Create individual and business end users, submit KYC identity data, and enroll them in one or more bank products in a single API call.

Virtual Accounts

Open segregated virtual accounts for each end user, query balances, and retrieve bank-assigned account numbers — all without touching the bank’s portal.

Domestic Wire Payments

Initiate ACH-like domestic wire transfers between virtual accounts or to external beneficiaries using simple debit/credit instructions.

International Wire Payments

Send cross-border payments in USD with support for SWIFT intermediary routing and correspondent bank details.

Internal Transfers

Move funds between accounts within the same Diameter tenant instantly, with no external payment rail involved.

Webhooks

Subscribe to real-time event notifications for account status changes, payment completions, and onboarding outcomes.

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Partner Banks

Diameter currently operates through two partner banks. When you create a Product (see below), you choose which bank backs it.
Partner bank availability depends on your tenant’s approved product configuration. Contact support@diameterpay.com to enable a specific bank or rail.

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Tenant and Product Model

Understanding the two-level organizational model is essential before making your first API call. Tenant Your organization is represented as a Tenant in Diameter. All API credentials, Products, End Users, and Accounts belong to your Tenant. When you call GET /v1/tenants/self you retrieve your Tenant’s configuration, approved products, and feature flags. Product A Product is a specific bank integration tied to your Tenant. Each Product maps to a single partner bank and defines the account type, currency, and compliance rules that apply to end users enrolled in it. Diameter supports two product models: When you onboard an end user you supply a productId to indicate which Product — and therefore which bank — the user should be enrolled in.

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API Versioning

The current stable version of the Diameter API is 0.11.7. All endpoints are prefixed with /v1/. Breaking changes will be released under a new major version prefix (e.g., /v2/) with a documented migration path and a deprecation window of at least 90 days. Include the x-idempotency-key header on all write requests to ensure safe retries. See the Quickstart for details.

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Getting Help

If you have questions about credentials, product configuration, compliance requirements, or anything else, reach out to the Diameter team: Email: support@diameterpay.com The support team typically responds within one business day. For urgent production issues, mark your email subject line with [URGENT].