Accessing NAS outside home network

Hi all

I am using Pro version on my Apple TV and it works like a charm. I am trying to use it on my iPhone but unable to access NAS while outside home network. I can access NAS using other apps. Port forwarding is done so that is fine, access is given. Only through Infuse I am unable to have access. Maybe I am missing something.
NAS is Buffalo Terastation 1200D. It is a bit older one but does the job for me.
Hopefully someone will have a good advice

Welcome to the forum. There may be some ideas in the users guide here.