Describe a specific, valid use case for employing a `PATCH` HTTP method within an OTP API, detailing what resource it would modify and why `PUT` would be less suitable.

A specific, valid use case for employing the `PATCH` HTTP method within a One-Time Password (OTP) API is to update the state of an existing OTP request resource, particularly when a user's verification attempt fails. An OTP API manages the lifecycle of One-Time Passwords, which are temporary authentication codes. A resource, in the context of an API, is an identifiable entity, such as an `otp_request`, exposed via a Uniform Resource Identifier (URI) that holds specific data and can be manipulated. For instance, an `otp_request` resource at a URI like `/otp-requests/{id}` might initially contain attributes such as a unique `id`, `user_id`, the actual `otp_code` (which should not be directly exposed or modified by clients), `status` (e.g., 'pending', 'sent', 'verified'), `expires_at` timestamp, and `attempt_count`.

When a user submits an incorrect OTP for verification, the API needs to record this failed event. The `PATCH` HTTP method is specifically designed for partial modification of an existing resource. In this scenario, only certain attributes of the `otp_request` resource require modification; for example, the `attempt_count` attribute needs to be incremented, and the `status` attribute might transition to 'failed_attempt' or 'locked' if a predefined maximum number of attempts is exceeded. A `PATCH` request to `/otp-requests/123` would send a concise payload, such as `{"attempt_count": 3, "status": "failed_attempt"}`, indicating precisely which fields to modify without requiring knowledge of the entire resource's current state. This method is efficient because it transmits only the changes, and it is precise because it targets only the intended attributes.

The `PUT` HTTP method is less suitable for this scenario because its fundamental purpose is to perform a full replacement of a resource. A `PUT` request requires the client to send a complete, updated representation of the entire resource, effectively overwriting the existing one. For the OTP verification use case, this would necessitate the client retrieving the current state of the `/otp-requests/{id}` resource, including sensitive or internal attributes like the `otp_code` itself or the `expires_at` timestamp, which the client typically neither possesses nor should modify. The client would then have to construct an entirely new representation of the resource, incorporating the updated `attempt_count` and `status` while ensuring all other existing, unchanged attributes are correctly included in the request body. If the client fails to include any existing attribute, or provides an incorrect value for an unneeded attribute, a `PUT` operation would inadvertently delete, reset, or corrupt that data on the server. This introduces complexity for the client, increases data transmission, and poses a significant risk of unintended data loss or state corruption, as it demands the client to manage the entire resource state accurately for even minor updates. `PATCH` overcomes these limitations by allowing granular, focused modifications without requiring knowledge or submission of the full resource representation.