Made more progress and found out the communication failure was due to network issue. Moved both the ESP8266 NodeMCU and the OS Pi to the base home LAN from the Eero network. That fixed it. Have not yet found out why being in the Eero network does not allow these two 2.4GHz devices to communicate with each other. At least I was able to get past the issue and have my sensor talk to the sprinkler and turn on the sprinklers using moisture data. The API works as advertised. Thought I would send in the follow-up in case others have similar issues.