capsul-flask/docs/btcpay.md

## <a name="BTCPAY_PRIVATE_KEY"></a>Setting up the BTCPAY_PRIVATE_KEY 

Generate a private key and the accompanying bitpay SIN for the btcpay API client. 

I used this code as an example: https://github.com/bitpay/bitpay-python/blob/master/bitpay/key_utils.py#L6

```
$ pipenv run python ./readme/generate_btcpay_keys.py
```

It should output something looking like this:

```
-----BEGIN EC PRIVATE KEY-----
EXAMPLEIArx/EXAMPLEKH23EXAMPLEsYXEXAMPLE5qdEXAMPLEcFHoAcEXAMPLEK
oUQDQgAEnWs47PT8+ihhzyvXX6/yYMAWWODluRTR2Ix6ZY7Z+MV7v0W1maJzqeqq
NQ+cpBvPDbyrDk9+Uf/sEaRCma094g==
-----END EC PRIVATE KEY-----


EXAMPLEwzAEXAMPLEEXAMPLEURD7EXAMPLE
```

In order to register the key with the btcpay server, you have to first generate a pairing token using the btcpay server interface.
This requires your btcpay server account to have access to the capsul store. Ask Cass about this.

Navigate to `Manage store: Access Tokens` at: `https://btcpay.cyberia.club/stores/<store-id>/Tokens`

![](images/btcpay_sin_pairing.jpg)


Finally, send an http request to the btcpay server to complete the pairing:

```
curl -H "Content-Type: application/json" https://btcpay.cyberia.club/tokens -d "{'id': 'EXAMPLEwzAEXAMPLEEXAMPLEURD7EXAMPLE', 'pairingCode': 'XXXXXXX'}"
```

It should respond with a token: 

```
{"data":[{"policies":[],"pairingCode":"XXXXXXX","pairingExpiration":1589473817597,"dateCreated":1589472917597,"facade":"merchant","token":"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx","label":"capsulflask"}]}
```

And you should see the token in the btcpay server UI:

![](images/paired.jpg)

Now simply set your `BTCPAY_PRIVATE_KEY` variable in `.env`

NOTE: make sure to use single quotes and replace the new lines with \n.

```
BTCPAY_PRIVATE_KEY='-----BEGIN EC PRIVATE KEY-----\nEXAMPLEIArx/EXAMPLEKH23EXAMPLEsYXEXAMPLE5qdEXAMPLEcFHoAcEXAMPLEK\noUQDQgAEnWs47PT8+ihhzyvXX6/yYMAWWODluRTR2Ix6ZY7Z+MV7v0W1maJzqeqq\nNQ+cpBvPDbyrDk9+Uf/sEaRCma094g==\n-----END EC PRIVATE KEY-----'
```

-----

## <a name="testing"></a>testing cryptocurrency payments

I used litecoin to test cryptocurrency payments, because its the simplest & lowest fee cryptocurrency that BTCPay server supports. You can download the easy-to-use litecoin SPV wallet `electrum-ltc` from [github.com/pooler/electrum-ltc](https://github.com/pooler/electrum-ltc) or [electrum-ltc.org](https://electrum-ltc.org/), set up a wallet, and then either purchase some litecoin from an exchange, or [ask Forest for some litecoin](https://sequentialread.com/capsul-rollin-onwards-with-a-web-application/#sqr-comment-container) to use for testing.


## <a name="0_conf_diagram"></a>sequence diagram explaining how BTC payment process works (how we accept 0-confirmation transactions 😀)

![btcpayment_process](images/btcpayment_process.png)

This diagram was created with https://app.diagrams.net/.
To edit it, download the <a download href="readme/btcpayment_process.drawio">diagram file</a> and edit it with the https://app.diagrams.net/ web application, or you may run the application from [source](https://github.com/jgraph/drawio) if you wish.