"Symplectic Publications API Base URL" 
"The base URL for the Symplectic Publications API (only supports v3.7.16) E.g., https://source.symplectic.host/publications-api/v3.7.16"

Is there enough room for that? Key improvements in the revised wording:

* Makes it clearer it's the symplectic publications api url
* Doesn't default to some internal cambridge dev instance url, while still providing an example URL