Check this link out:
You may be out of luck. About a year ago, Google changed a bunch of their APIs and it screwed up a lot of features and code. Anyways, up until fairly recently there was a notice up on the splash page informing users that some of DualSportMaps features no longer worked and an extensive recoding of sections of the program were necessary. Anyways, to make a long story short, he took it down as being available for purchase on Google Play because it wasn't fully functional any longer. I don't recall what features no longer were supposed to work, but everything I ever used it for still worked just fine.
Anyways, as it stood the last time I looked at it, if you'd already purchased and downloaded it, it was still there on Google Play for you to download again in the future. But if you hadn't already purchased it, Google Play detected that and would not display DualSportMaps. It may be a while - if ever -before the coder does the rewrite. The app costs him money as does the website to run, so fixing it amounts to another long and expensive freebee project. And on the other side of the coin, for the last while his interest has been on the development of a small hand controller which will run all the apps on his phone while riding. Everything else is second to that project for him, last time I was in contact.
The Android app and DualSportMaps.com are two separate but linked things. The website came first and it is still functional as ever. The Android app, as described above, has problems due to the API change but still works. You can upload and download .gpx files to the website from just about any platform; you do not need the app to do any of that.
Hope this info clarifies things for you.