I suspect the issue may lie with something in your ftp configuration…but it is only a suspicion. Can’t say with certainty without seeing screenshots of your ftp configs from your dashboard.
But even if I assume that you have setup ftp correctly, I noticed you talked about following the steps in that linksys document. I only skimmed the first half of it. I understand that you (or anyone else) would pay for getting a static WAN IP but I do hope you have assigned a static LAN IP on your router for the EX2 (which technically is reserving a DHCP IP for your EX2 but the idea isthe same - your EX2 gets a static LAN IP…and note, we are talking of LAN IPs, not WAN IPs). To be cleaer, this is something you’ll do on the router - on the link you gave, it is mentioned as “Setting up DHCP Reservation on the router”.
Once the LAN IP for EX2 is made static, you can use that IP anywhere you are asked to enter a server name (which in your pic is the first setting called Server) as long as you are within your network.
Anyway, I strongly recommend you first install an ftp client on your computer rather than do this from your phone and make sure it works from the computer first, Once you get it to work, simply use the same ftp connection settings in your Photosync app. Filezilla is an excellent ftp cleint app available for Mac and Windows. When installing do a custom install becase lately I have heard from folks that they try to sneak-install other 3rd party browser addons…so during custom install just decline any 3rd party stuff and just install the core filezilla client.
After that, try to connect via ftp usng your lan IP. If you have setup passive connection in your ftp config, filezilla should be able to connect using transfer mode as Auto (under Transfer settings tab), which is the default anyway. As long as you do all of this within your network, you do not need to setup ANY port forwardings…that only comes into the picture when you are coming in from outside…basically then you need to map what the outside ports will go to (i.e. forwarded to) which internal (LAN) IP.
As for SFTP, you cannot setup ANY username for sftp access othern than the one and only pre-defined SSH access username, as mentioned on page 122 of the maual using page number on the printed page (but actually is page 127 of the PDF). In the section titled SSH on that manual’s page, you will see what the SSH login username is in the last line of that section starting with the word Note. As I have said efore, you really shouldn’t do ay of this with SFTP. Unless you want to muck with Linux on EX2’s permission and path issues, which I’d guess you don’t want to (unless you are very familiar with Linux/Unix).