"Sound does not work using Amazon or any app accessed from the TV, picture is fine"
"picture is fine" signifies you already have internet access, if no Ethernet cable plugged in, then it must be wifi. You're good from here.
For sound, make sure you are enabling ARC on BOTH devices, TV and AVR.
On the AVR, make sure you select the correct input for ARC.
Can't help much unless you get all the basic connections/setups done.