GPost is a global technology, but is only available for download in certain countries.
The GPost app is currently available for download in the United States, Australia, the Netherlands, and the Bahamas via the App Store and Google Play Store. GPost is available for download in Haiti via the US App Store. If you are physically in these countries but the region of your Apple ID or Google Play ID is set to another country, then you will not be able to download the GPost app. If you change the country/region of your Apple ID or Google Play ID account and try again, you will be able to download GPost.