Citibuy will only allow one unique tax ID for every vendor profile. Since your tax ID already exists it is likely that another person from your company has already registered in Citibuy.

Citibuy does allow multiple users on one Vendor Account. If you need to be added as a user, please contact your "Seller Administrator" for your company. They may add you by clicking on the “Seller Administrator” tab in the upper-right corner of the web page after login.

If you need assistance identifying your "Seller Administrator", please open a help ticket on this portal.