SOS Father’s Day gift!

Okay ladies I think I made a mistake. My husband has an iPhone 6 Plus and I just bought him an iPhone series 3 watch but I’m now realizing that on most of the things I see it says it’s compatible with 6s. Does anyone know if it is compatible with 6plus as well? Im freaking out because I always fail with gifts

Update: I called apple and the sales rep told me his phone wouldn’t work with any watch. What I didn’t realize is it is a 6s plus instead of just a plus. I gave it to him it works and he loves it!