If the App Store says that your device is not compatible and therefore cannot be downloaded, this will most probably be because your device falls below the minimum required specification as shown in the compatibility section of the Site Report Pro product page on iTunes / App Store.
Please note that this is not our restriction, but a restriction imposed by Apple. Apple no longer permits 32 bit applications to be submitted to the App Store and Site Report Pro was first released after this restriction was put in place, meaning that there is no 32 bit version available for download.