In Rising Battle Level 2600, there is a condition that "only Vegetto can participate in the battle" in the sorter condition. "Vegetto only", but only SP Super Vegetto and SP Vegetto can be selected as battle members.
So if you don't have super vegetto, you need to orbit the level 2200 first, collect dedicated rising souls and super souls, and train vegetto up to level 2000. In addition to the dedicated soul, you will also need red rising souls, so collect them in a bonus battle.