While it is not possible to directly get potential reach data from Haiilo's API, you can use a simple formula to create the same results in your reporting.
Reach can only be calculated for LinkedIn and Twitter (X).
To calculate potential reach with Haiilo's API data, multiply the number of connections on a specific network for a specific user by the number of shares that the user performs on that network. You are able to get the share information from the GET/Shares endpoint and a user's connection information from the GET/Users endpoint.
If Sam has 500 connections on LinkedIn and he made 3 shares to LinkedIn during November 2021, his potential reach is 500 connections x 3 shares, so 1,500 potential impressions.