Characters with the acolyte background have additional benefits when using this option.
Acolyte Background. A character possessing the acolyte background requesting spellcasting services at a temple of their faith can request one spell per day from the Spellcasting Services table for free. The only cost paid for the spell is the base price for the consumed material component, if any is required.
Only some faiths are represented by temples large enough to provide this benefit. When playing any given adventure, the available faiths are determined by the season or region in which the adventure is set.
DDAL Dungeon Master's Guide v2.1, pp. 6-7