public function coinSelection($identifier, $outputs, $lockUTXO = false, $allowZeroConf = false, $feeStrategy = Wallet::FEE_STRATEGY_OPTIMAL, $forceFee = null) {
        $args = [
            'lock' => (int)!!$lockUTXO,
            'zeroconf' => (int)!!$allowZeroConf,
            'fee_strategy' => $feeStrategy,
        ];

        if ($forceFee !== null) {
            $args['forcefee'] = (int)$forceFee;
        }

        $response = $this->blocktrailClient->post(
            "wallet/{$identifier}/coin-selection",
            $args,
            $outputs,
            RestClient::AUTH_HTTP_SIG
        );

        \var_export(self::jsonDecode($response->body(), true));

        return self::jsonDecode($response->body(), true);
    }