how the Reserved and Unreserved spirit work?

hi guys, first of all, totally noobie here, so sorry for stupid question
I am following the next build in my first playthrough - https://maxroll.gg/poe2/pob/ff7ia0lx
as you can see, this guy has Spirit 270/212, and i even understand those numbers
212 is the base (112 from the body armour, Invoker ascendency)
and 270 is the cost of all skills he use
HoT 30s, Cast on Critical 90, Ghost Dance 30, Sacrifice 30, Blink 60
but I don't get it, when I am trying to activate the Sacrifice with my 210 spirit it says something like Not enough spirit
so how can i make all my spells active with only 212 spirit? can someone please explain it to me?
Comments
He us probably using blink on weapon set 2. So he is not reserving spirit when using weapon set1. So 270 - 60(blink) is 210 and that checks out