The national broadcaster has described it as a "serious breach of trust".
A review was carried out by Grant Thornton into RTÉ's accounts - which was discussed by the board of the broadcaster on Monday.
It found payments totalling €345,000 were paid to Ryan Tubridy between 2017 and 2022 - over what was made public.
The review found RTE had guaranteed additional payments to the former Late Late Show host through commercial partners in exchange for appearances.
Figures released by the broadcaster show Tubridy was paid in excess of €500,000 between 2017 and 2022, despite his salary being declared below half a million.
Ryan Tubridy stepped down as host of the Late Late Show earlier this year.
The RTE board has apologised.
