Warlock with level 2 spell slots cannot use level 1 spells

As a Warlock, you obviously have slightly different spell slot types to wizards. I am a Warlock with level 2 Warlock spell slots, but when I try to cast a level 1 spell, the game doesn’t think I have level 1 spell slots, not realising that I can use those level 2 Warlock spell slots for it.