On some makes and models of Android device, the default keyboard shown for numerical entry lacks a minus key (e.g. Samsung Keyboard). In this scenario, we recommend that you install the free Google GBoard keyboard from the app store.
The first step is to open the Google Play store on the Android mobile device. Tap on the icon shown in the image below.
Type google keyboard into the search bar and select the item shown below.
Tap the Install button to begin downloading the app.
Once the installation has been completed, tap on the Open button to begin the setup of the new keyboard.
Work through the setup steps shown onscreen. Tap Enable in Settings.
Then tap on the switch next to GBoard to enable id. The toggle will go blue when enabled.
Close the prompt that appears as shown below.
Tap on the Select Input Method button.
Now select GBoard.
The newly installed Google Keyboard should now be ready for use. It should now be possible to enter negative numbers as shown below.