Keyman for iPhone and iPad: Installing Custom Keyboards
Step 1) Click the link to your custom keyboard json file. (Note: typing the link into your browser URL bar won't work, you will need to include the link in a web page or email)
Step 2) Click 'Download'. This will fetch the keyboard and font specified from the json file:
The keyboard may also prompt you to install a font -- you should click 'Install' and follow the steps:
Once the keyboard has been downloaded, you should be able to use it as normal.
To learn how to create a custom installable keyboard, click here.