One of the players in our campaign has a 6th level Favored Soul. They have selected Versatile Spellcaster as their next feat; it reads:
You can use two spell slots of the same level to cast a spell you know that is one level higher. For example, a sorcerer with this feat can expend two 2nd-level spell slots to cast any 3rd-level spell [they know]. -- source
Does this effect chain? In other words, could the Favored Soul expend:
((Lv0 + Lv0 -> Lv1) + Lv1 -> Lv2) + Lv2 -> Lv3
to gain a level 3 spell? It would expend two level 0, one level 1, and one level 2, but would be extremely powerful at higher levels.
How does this work, and is this an acceptable use of Versatile Spellcaster? If so, are there any balance concerns to be aware of?