sipgate.io PUSH-API is available as an optional feature within your sipgate team account for a monthly fee of £29.95 GBP.
Account Administrators can book sipgate.io by logging into their online team account then going to:
Account Administration - Plans & Packages - Additional services from sipgate
Note: In addition to the sipgate.io, there is also the sipgate API.
The differences between the sipgate API and sipgate.io are explained here.