return http2SessionHandler.invoke()
            .catch((error) => {
              throw new FirebaseMessagingSessionError(error, undefined, undefined);
            })
            .then(() => {
              const requests = registrationTokensArray.map(async (registrationId) => {
                let requestPath = `/v1/projects/${projectId}/registrations/${registrationId}/topicSubscriptions`;
                if (isSubscribe) {
                  requestPath += `?topic_name=${topicName}`;
                } else {
                  requestPath += `/${topicName}?allow_missing=true`;
                }
                return this.messagingRequestHandler.invokeHttp2RequestHandler(
                  FCM_SEND_HOST,
                  requestPath,
                  httpMethod,
                  isSubscribe ? {} : undefined,
                  http2SessionHandler
                );
              });

              return Promise.allSettled(requests);
            })
            .then((results) => {
              if (results.length > 0 && results.every((r) => r.status === 'rejected')) {
                const firstReason = (results[0] as PromiseRejectedResult).reason;
                if (firstReason instanceof RequestResponseError) {
                  throw createFirebaseError(firstReason);
                } else {
                  throw firstReason;
                }
              }

              const response: MessagingTopicManagementResponse = {
                successCount: 0,
                failureCount: 0,
                errors: [],
              };

              results.forEach((result, index) => {
                if (result.status === 'fulfilled') {
                  response.successCount += 1;
                } else {
                  response.failureCount += 1;
                  const err = result.reason;
                  const errorCode = err.response?.isJson() ? getErrorCode(err.response.data) : null;
                  const errorMessage = err.response?.isJson() ? err.response.data?.error?.message : err.message;
                  const newError = FirebaseMessagingError.fromTopicManagementServerError(
                    errorCode || 'UNKNOWN',
                    errorMessage,
                    err.response?.isJson() ? err.response.data : undefined
                  );
                  response.errors.push({
                    index,
                    error: newError,
                  });
                }
              });

              return response;
            })
            .finally(() => {
              http2SessionHandler.close();
            });