Environment-specific assertions

What I often do in such a case is assert via a script assertion.

In the script I get the current active environment via:

def activeEnvironmentName = messageExchange.modelItem.project.activeEnvironment.name

//note, this is the name for your environment you have setup in the "Endpoints & Environments" setting.

//for tst

def expectedResult = "tst123"

if (activeEnvironmentName == "acc"){

//for acc

expectedResult = "acc123"

} 

then proceed with the actual assertion by getting the actual api response value and assert it against expectedResult

If you set up a Project level custom property, that will have a per-Environment value. If you then use a property expansion to that property as your XPath assertion's expected value, that should work. You can read more here.