How to install APKs on Gabb Plus?

I would like to install an APK (specifically Google Maps and a few others) on my Gabb Phone Plus. It uses a modified version of Android, and Samsung made the phone itself. I downloaded the APK from [Aptoide](https://en.aptoide.com/) and scanned it with [VirusTotal](https://www.virustotal.com/gui/home/upload) . Then, I put it on an SD card and transferred it to my phone. Once it was on my phone, I ran the APK. It didn't work. I tried it a few more times, and it said "Package installer keeps stopping." I tried to clear the cache, but couldn't. Then, I also force-quitted the app, and it didn't help at all. I am thinking that Gabb did something to this to prevent APKs from being installed. I tried looking this up on Google, but apparently, not many people have the Plus because it only showed results for the Z2. There must be a way to run APKs or put apps on the phone because I see Gabb installed their own apps on this phone.