Problem with rearview camera: it works only if P gear is selcted first

Hi all,

I'm new in the forum and I would kindly ask for a help.

I have an Octavia III SW of 2015 with DSG, I installed an aftermarket rearview camera, I activated it via long coding and it works, but... but it works only if before... I select the P and then the R gear.

Basically it works only with the sequence P -> R, any other sequence  it doesn't work (from D to R for example), I must always select the P and then R to see the camera on the screen.

Any suggestions?

Thx

Davide