Open Setup > Addon Modules and activate Telegram Addon. After activation check permissions and save settings.
Go to Addons > Telegram Addon and fill the License Key field.
Fill Bot Username and Token in the Bot Settings tab.
Select notifications you want to send.
Edit Client Notification if needed
Create Custom Admin Notifications (the will be used in Notification Module)
Admin Notifications
Go to Setup > Notifications click "Configure" on Notification for Telegram Addon.
You can add up to 5 Chats/Groups. To find Chat/Group ID open Telegram Web and open group info. Right click on Invite to group via link and copy link. Link will be like https://web.telegram.org/#/im?p=g370024601. Numbers is group ID with '-' sign.
Create new notification rule: select Recipient and Template