OK, then it's a cassette. The numbers are a US patent number and "tighten>40 N-m" which is the direction the ring tightens and the recommend tightening torque of 40 Newton-meters which is about 30 ft-pounds, i.e. quite a lot.

So. let's dispose of the obvious, is the lockring tight? If it has come loose, tighten it fully and see if that solves the problem.

Assuming it isn't that simple, you are in for a complete hub teardown to locate the problem Broken axles on freehubs are much rarer than on freewheel hubs but not impossible. At this point my best guess is a broken axle or a thoroughly destroyed bearing.