Wall of Sand’s description reads as follows (emphasis mine):
You conjure up a wall of swirling sand on the ground at a point you can see within range. You can make the wall up to 30 feet long, 10 feet high, and 10 feet thick, and it vanishes when the spell ends. It blocks line of sight but not movement. A creature is blinded while in the wall’s space and must spend 3 feet of movement for every 1 foot it moves there.
To me, it’s unclear whether or not the bolded clause provides total cover to a creature behind the wall, or if the creature is simply heavily obscured. If you and another creature are on the opposite sides of a Wall of Sand, can you perform a ranged weapon or spell attack against the creature?