Citizens whose nationality corresponds to countries members of the OECD (Organisation for Economic Co-operation and Development) do not need visa to enter Argentina for conferences. They can enter the country simply showing their valid passport.
Check the list of OECD countries here: https://www.oecd.org/about/document/ratification-oecd-convention.htm
If your country is not part of the OECD, you will most likely need a Visa to enter Argentina, and you will need an invitation letter to apply. We will soon be circulating an email with a form to collect information about the nationality and country of residence of those who will need a Visa, to write the corresponding invitation letters.