Rear brake must first be bled at the front calipers (linked system) , then you bleed it at the rear caliper.
You probably have air in the lines leading to the front caliper.
There are 2 bleeders on the front caliper, the bleeder pointing back to the engine is for the center caliper piston (rear brake link), the bleeder pointing up is for the front brakes.

I have always bled, front right caliper first, left front caliper second and then rear caliper third.