Hi
The Service Layer is a SAP add-on to B1 as I understand it. We have a partner that provides B1 and they setup the Service Layer for me. However there are no triggers from the SAP side. What you could do however is run a logic app on a reoccurrence schedule and filter the ODATA to give you accounts or contacts that were created since the last run of the LA. It's not an elegant solution but there is nothing on the Service Layer that will invoke a trigger.