API Reference Overview - Nucleus Core Banking

The Nucleus Core Banking API provides complete programmatic access to all banking domains.

Interactive API Explorer

Mintlify natively renders the embedded OpenAPI 3.0 specification (openapi.json). You can inspect request schemas, parameter constraints, and live responses across all core modules:

Clients & KYC

CIF records, identity documents, BVN linking, and addresses.

Savings & Deposits

Savings accounts, fixed deposits, interest charts, and overrides.

Loans & Credit

Loan products, origination, appraisal, approvals, and schedules.

Tellers & Cash

Cashiers, cash drawers, deposits, withdrawals, and allocations.

Accounting & GL

GL accounts, journal entries, rules, and financial closures.

Self-Service Banking

Headless APIs for custom iOS/Android mobile and web apps.

Global Response Codes

Status Code	Description
`200 OK`	The request succeeded and returned requested data.
`201 Created`	The entity was successfully created (returns resource ID and CIF/account numbers).
`400 Bad Request`	Validation failure (e.g. invalid date format, missing mandatory parameter).
`401 Unauthorized`	Invalid credentials, expired session token, or missing tenant header.
`403 Forbidden`	Domain rule violation (e.g. onboarding at HQ instead of branch, maker self-approving).
`404 Not Found`	Target resource does not exist under the active tenant.
`409 Conflict`	Concurrency or duplicate constraint violation (e.g. duplicate CIF or external ID).
`500 Internal Error`	Unexpected server fault (reported with correlation tracking ID).

Standard Error Response Payload

{
  "developerMessage": "The request was invalid. A specific parameter failed validation.",
  "httpStatusCode": "400",
  "defaultUserMessage": "Validation errors exist.",
  "userMessageGlobalisationCode": "validation.msg.validation.errors.exist",
  "errors": [
    {
      "developerMessage": "The parameter officeId is mandatory.",
      "defaultUserMessage": "The parameter officeId is mandatory.",
      "userMessageGlobalisationCode": "error.msg.client.officeId.cannot.be.blank",
      "parameterName": "officeId",
      "value": null
    }
  ]
}

​Interactive API Explorer