When you create a new posting campaign, you need to specify your Telegram bot token. Press the Authenticate button for this.
When you authenticate your bot, we check its recent actions (like posts, name/link changes, if it was added to any channel or group recently). And we show you the list of your channels and groups with recent actions in the Send posts to drop-down. In this list, we also show channels and groups used in your other Telegram posting campaigns.
If no actions were made in the channel or group lately and you don't use it in any other posting campaign, most likely it won't be visible on the list. The easiest way to add it to the list is to go to your channel/group and make a manual post (you can remove it right away). Or you can remove and add your bot there. Then press Authenticate and you will see your channel/group in the list.
Another way is to manually add your channel or group ID. But since it is not an easy task to find out this ID, we would recommend using the method mentioned above. But if you still prefer to add a channel or group manually, please find the Other channel/group option at the bottom of the dropdown list.
Please note, you can manually specify your public channel by its ID (-NNNNNNNNNN) or URL (https://t.me/my_public_channel), but you cannot add invite links of private channels or groups there. However private channels and groups do have IDs as well. You can see these IDs in the web address bar in the Telegram web client (https://web.telegram.org/) in any browser: