That is the most mature Slack Module for WHMCS. It does not only look nice, it also has some cool features! Here are the key features:
It is useful when you always know what happens in your system. With the Slack for WHMCS module you dont need to refresh the page every 15 minutes to see that there is a ticket waiting for reply. Now you get instantly notified if something happens on your system. You can choose on which events you get alerts, also you can post messages to different and multiple channels or persons.
Unlike other modules, this module does not post the message directly to slack. It does maintain a message queue.
Why a message queue is useful?
If you send messages directly to Slack, there will be a small delay at the page load time for the customer. Your WHMCS Installation will wait until Slack processed your request. Much worse it goes if the slack service is not reachable from your server or the request times out. Then your clients will have a long page load time delay until the API request time outs. But you dont need to care about such cases with this module!
Your own Sender API
With this module you get your own sending API. You can send messages from your own scripts to the slack channels and also can integrate external services with your own, easy to use, HTTP based API. The HTTP based API can be useful if you want to integrate an external monitoring service (like Zabbix or Nagios) into slack.
The best place to start if you need help with a specific product is to contact the developer. All WHMCS Marketplace developers have both a website and support URL listed.
MSG91 WHMCS SMS plugin gives you the power and flexibility to stay connected with your customers by sending them an SMS and OTP's for 2FA at the crucial steps that matters the most.
Transactional email support for Sendgrid, Mailgun, Postmark, Sendinblue, Mailjet, Sparkpost, Mandrill and AmazonSES
More Advanced SMS System (Two-Factor Authentication)
Netgsm Sms addon provides you sending customized bulk sms and creating sms templates.
Professional business e-mail for your users