Use the debugger as shown below via the REST Lab.
Debugger use is intended for developer servers, since database locks and other resources are held while execution is paused.
To set a breakpoint, enter the REST Lab, and
These breakpoints are local to your API Key, and are saved across requests.
Set the Debug option, and run a transaction as shown below.
When you issue the update, execution will pause at your breakpoint, and you will see the screen below.