E-Commerce Tech Valuation

Hey guys, im stuck in a pickle here. wondering if anyone can help me out. would be greatly appreciated. anyways I am currently trying to value this e-commerce company as well as justify a valuation for the company. its not publicly listed and they're a client of ours. I understand that there are all this industry specific metrics but how do i link it to the valuation. Lets say for instance this company is trying to get a valuation of $100m. given all the industry metrics how do i link it back to the valuation. Like for instance revenue/clicks, revenue/active customers. how do i really go on about coming up with a valuation for this? and also what are some other e-commerce valuation metrics. Im really struggling trying to link the metrics to derive a value.