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If a user does not have permissions to add a user group to a channel, they still would be able to see the channel in the listing, or see the group when they’re in the Add members modal, but they will get an error that they don’t have sufficient permissions to add the user group to a channel as displayed below explaining which permissions they lack.
These can be 3 or a combination of them as mentioned above.
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Adding permission setting to Manage Channel membership for user groups.
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