What kind of connection do you have? Do you have a fixed IP?
If you don't have a fixed IP, you have to create your own DNS server by using a server you have access to that has a fixed IP (that can be done for free, just use one of those free domain hosting services or a server of a befriended business or something, it's only for DNS, so noone should really care and there is no security risk). That will route the incoming connections to your variable IP. If you have a fixed IP, you don't have to do that, then your domain will be linked to your IP, or you'll know what your IP is at all times and can put that in the app.
Then you need to set up a DMZ that routes the calls for a particular port that you configure your app for and a particular alias to one particular box, which can be virtual, but when there are a lot of connections, that's not always the most economic solution, but you can definitely start with a VM. Then you need to decide on the protocol. That can be something simple like SFTP, which is probably not such a bad thing if it's only a simple data file that just needs protection from data corruption or MIM, but there are other solutions. Let's say you have to secure a DMZ, update your own DNS tables and provide an SFTP server, that can all be done on one machine that is used as a firewall, a router, and runs a VM with a minimal distro that provides a basic SFTP server. And that machine doesn't even have to be that powerful. I would take something lean and mean like Vector Linux or another Slackware based minimal setup on a recycled PC, anything less than 6 years old or so, so that it's easy to configure and you always have an overview of what's happening, less is more for servers. Then change the alias to rout the reporting to your mail address, so that you get all the important warnings per e-mail if something goes wrong, and you use a specific e-mail account for that (gmail also takes care of that for free).
There are also units that can act as a cloud FTP server, like from WD, and they provide a DNS service, so that even if you have a variable IP, your device will always be found. I don't know how secure these things are, because I don't have one and have never played with one, but they are not expensive, and if you have a decent router with flashable firmware or really good firmware, it will probably have a DMZ function also, that allows you to route the domain of your cloud-enabled device to only that device, and isolate it from the rest of your network. I just prefer things that can be custom configured because they make me feel safer, but it might well be that those devices are enough, depending on how much calls for the file at once there are, and whether you want instant reporting or not.
