One of the potential challenges of using synchronous communication in microservices is that it can lead to increased latency and reduced scalability. 

Since the requesting service has to wait for a response from the receiving service before continuing with its own processing, delays in the communication between services can result in slow overall performance.

 Additionally, if the receiving service is unavailable or takes a long time to respond, the requesting service may become blocked and unable to continue processing requests, which can limit the overall scalability of the system.

https://greeeg.com/en/issues/microservices-patterns-synchronous-vs-asynchronous