Hi @chris brin ,
- Does the issue exist in Outlook desktop or Outlook on the web?
- What type of account are you using? Are you using a 365 account? If you are using microsoft365 account, may I confirm whether other owners/members also cannot add member?
- Besides, contact the admin to help you add members in admin center, for detailed steps, please view below: Go to Groups > Groups > select the group > Members, then click View all and manage members button under Members section, in the pop out page, click Add members.
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