async def METHOD_NAME(self, r):
    from electrum.paymentrequest import make_request
    key = r.match_info['key']
    request = self.wallet.get_request(key)
    if not request:
        return web.HTTPNotFound()
    pr = make_request(self.config, request)
    return web.Response(body=pr.SerializeToString(), content_type='application/bitcoin-paymentrequest')