Thanks for the latest video. I followed the same steps. I hit another error when it calls access_token, though at APS side, the call has been succeeded. I suspected the issue came from the connecting of Zaiper.
After checking, it looks the request template affected. There is a request header Authorization with access_token, but when getting access token, this is NOT needed. After removing it from the template, connecting account and getting access_token succeeded.
Of course, when testing specific API such as BuildingConnected API, the header with Authorization is required. I manually added with the value=access_token. Then it works well to fetch API data such as getting companies info.
Could you give it a try? My test video is at