It's normally if Okta detects another account with the same 'firstname' and 'surname' values in either Okta or AD.
Also can you check you have 'Create Users' ticked under 'Directory Integrations' > 'Settings'.
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Facing the same issue however I don't see any option to move forward except ignoring this user. I want to create a new account as i am not able to find out any other account with same first name and last name but i cannot do that