Can’t write imei to sm-n900a OC1. Can’t root?

So a customer brought me a sm-900a, and it’s on OC1 (5.0 lollipop ).Octoplus tells me I need to root first, but I can’t seem to find a way to do so. Has anybody been able to root a stock OC1, or even downgrade successfully from OC1 to something lower that can root? I’m kind of at a loss here.