public function setTransactionMethod($method)
    {
        // check if is array
        if (!is_array($this->transactionMethods)) {
            $this->transactionMethods = [$method];

            return $this;
        }

        // check if method is already in array
        if (!in_array($method, $this->transactionMethods)) {
            $this->transactionMethods[] = $method;
        }

        return $this;
    }