What’s causing this chain to slip on the freewheel?

Picked up a white industries freewheel for $8 and have just installed it, it’s 18T and I’ve been running a 1/8” half link chain. Googling says this freewheel should accept both 1/8 and 3/32.

By slipping I mean the individual links catch on the tooth before slipping into place properly, you can hear it when you pedal. Is this more likely due to using the wrong chain or poor alignment?

Thanks!