public function addPromise(
        ClientRequestInterface $request,
        callable $startingSuccessCallback = null,
        callable $startingFailCallback = null
    ): ApiResponseInterface {
        $return = $this->promises[$request->getIdentifier()] = $this->createStartingPromise(
            $request,
            $startingSuccessCallback,
            $startingFailCallback
        );

        return $return;
    }