Optimization – How to better capture and sync data between a mobile app and a web REST API?

I am facing the following scenario:

We have a largely offline mobile app that serves to register and store medical records from locations with little to no connectivity. These records are recently being synchronized with a particular web server that implements a REST API. The case is that many requests are generated by all mobile agents that synchronize data with API endpoints, such as: B. Many requests for POST / medical records. In some cases we make one request per record, in other cases we stack the records and send blocks.

What I am currently interested in is whether there is a better, known approach to reducing the number of requests and the data transferred between the server and the mobile app in these or similar scenarios.