why is sidesync not working on my Mac? My phone and computer dont recognise each other.

[AC Question]

I am using Sierra OS and Android 6 and when i connect my Samsung S6 Edge+ via USB, the only thing that happens is my phone continuously asked for permission to create an MTP connection. I keep pressing allow but nothing happens. I don't even know if the devices are recognising each other or if my phone is simply responding to the USB plug in. If anyone has any ideas, i'm wide open.

Thanks

Crowntime8