haven't purchased one yet! looking at the roadtop ones, this the one ive been eyeing

Road Top Wireless Carplay Retrofit Kit Decoder for BMW i3 https://www.amazon.com/dp/B087R9LZBV/ref=cm_sw_r_cp_api_glt_fabc_K4CNQN3NYNJG5E5G9VYR

Road Top Wireless Carplay Retrofit Kit Decoder for BMW i3 I01 NBT System 2012-2017

I have a '14 and bought this one, works great.