Backup & Migrate path for restore

I can't upload a file throught backup & migrate. I already increased 

client_max_body_size 

and restarted both nginx and php services

but it still says 

413 Request Entity Too Large

So my plan is to upload via SFTP and then restore through the WebUI.

the thing is... where should I put the backup file in order for it to be restored with the WebUI?

thanks!