# HTTPS Transport Mechanism for DPP

## Abstract

[BRC-27](/payments/0027.md) defines an abstract messaging protocol that facilitates payments on the Bitcoin SV network. This specification extends the protocol with the specifics required for a concrete HTTPS implementation that includes message size limits and HTTPS-specific implementation details.

## Motivation

HTTPS is one of the most widely used transport mechanisms for internet traffic. Enabling users of HTTPS to benefit from the use of the [BRC-27](/payments/0027.md) DPP will facilitate increased industry adoption and growth. Defining implementation-specific stipulations for HTTPS-based DPP will address problems and ambiguities specific to this communications substrate.

## Specification

### Status Note

BRC-55 is the HTTPS transport for BRC-27 DPP. It is not implemented by the current `bsv-blockchain/ts-sdk` or `bsv-blockchain/wallet-toolbox` wallet substrates. Do not confuse the DPP `/api/v1/payment/{paymentID}` routes below with current BRC-100 wallet HTTP routes such as `/createAction` and `/internalizeAction`, or with BRC-105/BRC-121 402 payment headers.

Treat this document as external or legacy unless a deployment explicitly opts into DPP.

Below is the table with messages requested from client (wallet) to merchant (server).

The `paymentID` parameter is assumed to be known as a result of request between client-server before DPP protocol operation.

| MESSAGE      | ENDPOINTS                          | TYPE/SUBTYPE     | RESPONSE CODES                                                                                                                                                                                                                                    |
| ------------ | ---------------------------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| PaymentTerms | GET `/api/v1/payment/{paymentID}`  | application/json | <p>200 – contains PaymentTerms JSON object with all data used by the payee to construct a transaction<br>404 – returned if the paymentID has not been found<br>500 – returned if there is an unexpected internal error</p>                        |
| Payment      | POST `/api/v1/payment/{paymentID}` | application/json | <p>201 – contains PaymentACK JSON object<br>400 – returned if the user input is invalid, usually an issue with the paymentID<br>404 – returned if the paymentID has not been found<br>500 – returned if there is an unexpected internal error</p> |

PaymentTerms messages larger than 10 MB should be rejected by the wallet application, to mitigate denial-of-service attacks.

Payment messages larger than 10 MB should be rejected by the payment host’s server, to mitigate denial-of-service attacks.

PaymentACK messages larger than 11 MB bytes should be rejected by the wallet application, to mitigate denial-of-service attacks. This is larger than the limits on Payment and PaymentTerms messages as PaymentACK contains a full Payment message within it.

## Implementations

The BRC-55 API is implemented [in this example from Jad Wahab](https://jadwahab.github.io/direct-payment-protocol/#/).


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