Normally this error comes up when the group ID is changed due to the conversion into a supergroup. As this happens automatically when you give users admin rights you'll need to reselect the Chat Id in the Telegram action step.
Additionally, I’m not really familiar with Telegram groups that much. However, I found this blog from Telegram that refers about admins and supergroups: https://telegram.org/blog/supergroups?setln=en
Normal groups support up to 200 members while supergroups can have 200,000. supergroups also offer features like message pinning and better moderation, great thing for large communities.