HELP!! Problem running REL sub with Croft Phono Integrated

Hey guys, need some help here. For whatever reason I can’t get the REL speakon connection to work between my Croft Phono Integrated and my REL T5i. I can use the line out via coax but would like to be able to use the speakon. I’ve tried putting black cable on the red speaker posts and the phone ground. I know on the Croft black and red are reversed. I’m just getting no output. I’ve tried this sub with a couple other amps with speakon and it works perfectly, just wondering what could possibly be the issue here.