Almost every houseplant that dies indoors dies of light, not water. The trouble is that eyes adjust and rooms lie: a hallway that feels bright to you is dusk to a fiddle leaf fig.
The shadow test settles it. At noon, stand where the plant will live and hold your hand a foot above a sheet of paper. A sharp-edged shadow means bright light. A soft, fuzzy one means medium. If there is barely a shadow at all, that is low light, and you want a philodendron or a pothos rather than a cactus.
Do it again in December. A south-facing sill in summer and the same sill in winter are two different places, which is why the care card in the box gives a summer figure and a winter one.