Information on creating a Splashtop JSON can be found here under the installation files heading:
Navigate to your Profiles tab and click the plus sign under Available Payloads.
Select Android and then File
Note: In 6.2 all files must be stored under C:\Program Files\Wavelink\Avalanche\centralfilestore\files
Name your payload, select Add/update file, specify the file path for your particular device type (/enterprise/usr/persist (For Zebra), /persist (For Non-Zebra), or /sdcard (alternate path for non-zebra without persist folder)), click the search icon under File and select your file, and click Save
Your file payload will now show under Available Payloads