To a point, some slap is acceptable. Having said that, there is some modification that should be done in your form. More times than not, it is caused by torque by gripping the bow so tight, that you are twisting it at the shot. That kind of thing occurs before the arrow is released, a more closed stance would help. By that I mean turning both feet fast quatering toward the target, creates more room between the forearm and the bow string.
For hunting, I often just tape my bowarm sleeve down, just to keep the string from striking the clothing when the shot is taken. A good bow will give more of it's energy to the arrow when the string stays in contact with the arrow for a longer time. When my sting strikes my wrist, I don't worry. The arrow and the bow have done it's work by that time, it is when the string strikes the forearm that I have problems. I can most often trace it back to my foot position opening up. I hope this helps some.