Vallo was first recognised in a senior national team nomination on 16 March 2022 by Štefan Tarkovič as an alternate defender ahead of two international friendly fixtures against Norway and Finland.[3] When Francesco Calzona took over from Tarkovič in the summer of 2022, Vallo was called-up for two September 2022–23 UEFA Nations League C fixtures.[4] He made his debut on 22 September 2022 at Štadión Antona Malatinského in a fixture against Azerbaijan, which concluded in an upsetting 1–2 defeat following a stoppage time drama. Vallo completed the entirety of the match.[5] In a subsequent match against Belarus, Vallo remained benched.[6] He was also nominated for November friendlies against Montenegro and Chile, suffering an injury in the first match,[7][8] as well as prospective player's training camp at NTC Senec in December.[9]