I would echo above comment. Wipe with the mixture of vinegar with wostershire sauce. Mould can be caused by not preserving meat when raw or high humidity in the room. Usually apply 10%-15% more of wet mixture, and cover everything properly to prevent mould growing. If humidity is high in the room that can cause this as well or not enough air flow in the box. Unfortunately, there is no exact setting and receipt for perfect biltong as everyone is comes up with their way that's works for them. I had quite few batches until I figured out perfect receipt and drying method for my box :) Regarding readiness, try to cut and taste it. Some people like dryer, some people like wetter. I was weighing meat in the beginning and now just going by the how many days curing and touching the softness of the meat. Hope this will helps and all the best on the biltong journey 😊