I think you need to use/setup a group chat for telegram actions.
extract from Telegram - Actions | openHAB
That is the chatId. Note that if using a Telegram group chat, the group chatIds are prefixed with a dash that must be included in the config file. (e.g. bot1.chatId: -22334455)
In definition of telegram binding ( Telegram - Bindings | openHAB ) either group chats or comma separated list of chat ids can be used.