DOGTEK Extra Collar For Canicom 400 Na OS

I bought the DogTek 400 because I needed two collars; however, I can't get them to both operate individually. Using one collar works great, but can't use them on both my dogs at the same time. We only had to use the flash button a couple of times on the low setting to correct our dogs and now we just use the beep and they immediately stop misbehaving. If I could get them synced to use together I would rate them at 5 stars