Alpine Halo 9 Sub Out RCA

[BigL88]

Hi all, I installed a Halo 9 in my T6 today. The amp only picks up sound if the RCA’s are connected to the “front speaker out” RCA’s and nothing when connected to the “Sub Out” RCA’s. Thing is I want to LPF the front speakers so the Sub handles most the bass. Any ideas why the Sub Outs wouldn’t work please?

Thanks in advance

 

[Lightrofit]

Have you turned the sub output on in the sound settings?