From 27596e171bea5dea2edd22681070db82b0da852e Mon Sep 17 00:00:00 2001
From: Masaharu Hattori <112887632+Masa8106@users.noreply.github.com>
Date: Mon, 15 Jun 2026 13:01:20 +0100
Subject: [PATCH] Add HowtoUseAPI.md file

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+# How to Use the Number Recycling API
+
+## Introduction
+
+This supporting document presents the flow diagram on how to use the Number Recycling API from API consumers perspective.
+
+## Flow Diagram
+
+
+```mermaid
+    flowchart TD
+        A["t0<br/>API Consumer onboards the user and verifies the phone number<br/>(e.g. SMS OTP / Number Verification / equivalent trust step)"]
+        A2["API Consumer establishes a Trusted Reference Date<br/>(e.g. t0) and MAY store it according to its own policy"]
+
+        B["tn<br/>A sensitive action or hygiene check requires a phone-number trust assessment"]
+        C["API Consumer calls Number Recycling<br/>with specifiedDate = Trusted Reference Date selected by consumer policy"]
+
+        D{"API response"}
+
+        E["200 OK<br/>phoneNumberRecycled = false"]
+        F["200 OK<br/>phoneNumberRecycled = true"]
+        G["400 OUT_OF_RANGE<br/>specifiedDate is not processable for this provider/period"]
+        H["Other API errors<br/>(e.g. INVALID_ARGUMENT, SERVICE_NOT_APPLICABLE, auth errors)"]
+
+        E1["No recycling detected since specifiedDate"]
+        E2["API Consumer applies its own policy<br/>(e.g. proceed, or combine with other signals if needed)"]
+        E3["If the consumer establishes a new trusted point,<br/>it MAY define and/or store a new Trusted Reference Date"]
+
+        F1["Recycling / ownership change detected after specifiedDate"]
+        F2["Do not assume the same user still controls the number"]
+        F3["Apply mitigation according to business policy:<br/>block, step-up, re-verify identity, ask for updated phone number"]
+        F4["If a new or re-confirmed number is verified,<br/>the consumer MAY define and/or store a new Trusted Reference Date"]
+
+        G1["No business conclusion can be drawn from Number Recycling alone"]
+        G2["Use fallback path according to API consumer's policy:<br/>alternative factor, fresh verification, or re-enrolment flow"]
+        G3["If trust is re-established,<br/>the consumer MAY define and/or store a new Trusted Reference Date"]
+
+        H1["Handle according to generic API error policy"]
+
+        Z1["Note 1:<br/>This diagram is illustrative consumer guidance,<br/>not normative API semantics"]
+        Z2["Note 2:<br/>The Trusted Reference Date is not mandatory to store;<br/>it is chosen according to the API consumer's policy"]
+        Z3["Note 3:<br/>Examples may include original onboarding date,<br/>last successful reverification date, or another trusted timestamp"]
+        Z4["Note 4:<br/>false means 'no recycling detected since specifiedDate';<br/>it does not by itself prove current possession/control"]
+
+        A --> A2 --> B --> C --> D
+        D --> E --> E1 --> E2 --> E3 --> B
+        D --> F --> F1 --> F2 --> F3 --> F4 --> B
+        D --> G --> G1 --> G2 --> G3 --> B
+        D --> H --> H1 --> B
+        
+        Z1 -.-> D
+        Z2 -.-> A2
+        Z2 -.-> C
+        Z3 -.-> A2
+        Z4 -.-> E1
+``` 
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