If a person has left the group in the past, you need to be in their Telegram contacts to add them back.
They can still join via an invite link as long as they are not on the group's invite link as long as they are not on the Removed Users list.
194
抱歉，该用户已决定退出此群组，您无法添加该用户回来。
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Taylor Fung,
Aug 21, 2019 at 04:20