spell slots
Scrolls - bg3.wiki
A level 1 spell fits into a level 1 spell slot, but a level 2 spell is too large for a level 1 slot – you can’t use lower-level spell slots to cast higher level spells.
Ranger - bg3.wiki
Rangers are primarily martial fighters; they gain Spell Slots at 1/2 the rate of a full spellcaster. ... Spellcasting Level 1 Spell Slots Unlocked: 2 You gain two Level 1 Spell Slots.
Artificer Multiclassing and Spell slots - forums.giantitp.com
The Revised 5.24e Artificer Spell Slots per Spell Level.