Hi, Mark.
Our REST API returns JSON data format, and our Event Aggregator can read this JSON data to import from Site A to Site B if both are running The Events Calendar (TEC). It’s a bit more high-fidelity importing than straight iCal importing (which could also be done from one TEC site to another).
After writing all that, I think you’re actually asking about the full CRUD functionality of the REST API, including creating.
I’d suggest going through https://theeventscalendar.com/knowledgebase/introduction-events-calendar-rest-api/, particularly the self-documenting Swagger part for details.
After doing so, please let me know how things go for you.