FP-100c black images

So what am I doing wrong all the instant photos are black as in no image.I am using a light meter and have exposed 8 prints and all are black?I am using rz67 and late model polaroid back.

Usually if they are black they have not been exposed.

Dark slide still in place? Check the manual you may have to do something like set it for multiple exposure for a polaroid back.

Thanks I tried another pack and works fine.Contacted Amazon and they are sending a replacement pack at no charge.