@Override
    public void doAlarm(List<AlarmMessage> alarmMessages) throws Exception {
        Map<String, SlackSettings> settingsMap = alarmRulesWatcher.getSlackSettings();
        if (settingsMap == null || settingsMap.isEmpty()) {
            return;
        }

        Map<String, List<AlarmMessage>> groupedMessages = groupMessagesByHook(alarmMessages);
        for (Map.Entry<String, List<AlarmMessage>> entry : groupedMessages.entrySet()) {
            var hookName = entry.getKey();
            var messages = entry.getValue();
            var setting = settingsMap.get(hookName);
            if (setting == null || CollectionUtils.isEmpty(setting.getWebhooks()) || CollectionUtils.isEmpty(
                messages)) {
                continue;
            }

            for (final var url : setting.getWebhooks()) {
                final var jsonObject = new JsonObject();
                final var jsonElements = new JsonArray();
                for (AlarmMessage item : messages) {
                    jsonElements.add(GSON.fromJson(
                        String.format(
                            setting.getTextTemplate(), item.getAlarmMessage()
                        ), JsonObject.class));
                }
                jsonObject.add("blocks", jsonElements);
                final var body = GSON.toJson(jsonObject);
                try {
                    post(URI.create(url), body, Map.of());
                } catch (Exception e) {
                    log.error("Failed to send alarm message to Slack: {}", url, e);
                }
            }
        }
    }
Use SkyWalking alarm slack webhook API calls a remote endpoints.
oap-server/server-alarm-plugin/src/main/java/org/apache/skywalking/oap/server/core/alarm/provider/slack/SlackhookCallback.java