Model

The Platform’s model is one set of conventions: how money, dates and identifiers are written, and which figures are derived rather than stored. The Platform records what you report, prices the agreement once at issuance, and derives every later figure from the two. Nothing recorded is edited or deleted; a withdrawal is itself a fact, and the withdrawn one stays readable while contributing to nothing. No scheduled job posts a figure.

Values

Four fields on a Loan, a Receipt or a Client carry an instant, and each ends in _at. Every other date-bearing field carries a civil date, whatever its name: anchor, value_date, due_on and the on an event body takes. Five values carry a fixed form on the wire.

Value	On the wire	Rule
Amount	`{"minor_units":125000,"currency":"MXN"}`	An integer count of the currency’s minor units: this one is MXN 1,250.00, and a decimal is refused.
Currency	`"MXN"`, inside every Amount	An ISO 4217 code, matched exactly, that fixes how many minor units make one unit.
Rate	`"45.5"`	A decimal percentage in a string; `rate` and `penalty_rate` are per year, and a JSON number is refused.
Date	`"2026-03-02"`	ISO `YYYY-MM-DD` carrying no time and no zone; a timestamp is refused rather than truncated.
Refusal	`{"error":"<prose>"}`	Prose with no code and no type on every refusal a route answers, so a client branches on the HTTP status.

One issuance body carries every form, and a refused request answers the fifth.

{
  "reference": "loan-2026-03-02-8841",
  "client_id": "client-8841",
  "configuration_id": "0f7c9a1e-3b6d-4a52-9f10-27c4d8e5b3a6",
  "configuration_version": 3,
  "principal": { "minor_units": 800000, "currency": "MXN" },
  "term_periods": 12,
  "rate": "45.5",
  "penalty_rate": "60",
  "anchor": "2026-03-02",
  "jurisdiction": "MX",
  "tax": { "rate": "16", "on": ["interest", "fee"] }
}

{
  "error": "loan: selected term is outside the configuration"
}

Fields

A Reference is your own identifier for one issuance or one reported Receipt, and the first request carrying it answers 201. Every path begins /v1/tenants/{tenant_id}/, and a key acts for that one Tenancy. Each identifier is chosen by one side, has one shape, and behaves one way on a repeat.

Field	Chosen by	Shape	On a repeat
`id`	You	A Client’s identifier, 1 to 64 characters of letters, digits, hyphen and underscore, named `client_id` elsewhere.	The same `label` answers `200`; a different or omitted one is refused `409`.
`reference`	You	The same grammar, unique within your Tenancy for each kind of record.	The same statements answer `200`; the first that differs is named and refused `409`.
`loan_id`	The Platform	A UUID, and the only address a Loan answers to.	Not applicable.
`configuration_id`	The Platform	A Product’s UUID from `/product-configurations`, sent with `configuration_version`.	Not applicable.

A statement the retry omits is compared as none, so dropping a field the first request carried is refused rather than replayed.

Derivation

A read that answers as of a date names it in the query parameter on. A request without it is refused, because the Platform chooses no date for a lending read. A date that has not arrived is answered. Each figure is either computed at issuance and stored, or derived by the read that asks for it.

Figure	Where it comes from	What changes it
The Schedule, and each Period’s principal, interest, fee and tax	Computed at issuance and stored	Nothing rewrites the stored rows; a borrower’s Election re-plans the Periods inside the as-of reads.
A Loan’s state	Folded from that Loan’s recorded facts on every read	Recording a fact about the Loan or withdrawing one, and reporting or reversing a Receipt that discharges it.
An Allocation	Recomputed from your reported Receipts in value-date order	Reporting a Receipt, or reversing one.
Arrears	Derived for the date the request names	Any fact value-dated on or before that date, whenever it was reported.

Invariants

Five properties hold across every figure the Platform reports.

Derived. Every figure is derived from the facts on record.
Not accumulated. No figure is stored as a running total.
Not edited. A wrong fact is withdrawn rather than changed, and every figure is re-derived without it.
As-of. The Platform derives a dated figure for the date your request names, and for no other.
Versioned. A Product change never disturbs a Loan already issued.

Restrictions

Seven refusals follow from the conventions above.

No write except an issuance and a reported Receipt carries a Reference, so a retried cancellation, acceleration, write-off, retraction or reversal is refused 409.
No Reference guards Product creation, which writes a second Product on every request rather than replaying.
No Reference is spent by a request the Platform refused.
No figure the Platform cannot state arrives as null: the field is omitted, and anomalies names why.
No amount is converted, because two currencies never meet in one operation.
No Arrears are derived for a date before a Loan’s anchor, and the payment-options read leaves such a Loan out.
No route paginates or sorts, and no list narrows except Loans, by client_id.

API reference

Product configurations

Values

Fields

Derivation

Invariants

Restrictions

​Values

​Fields

​Derivation

​Invariants

​Restrictions

Values

Fields

Derivation

Invariants

Restrictions