Query:

Customer is planning to set up Database Mirroring for High Availability in his test environment. In SQL 2016 version is this supported?

Response: 

Database High availability is the concept related to RDBMS and not with iVend application. 

Below are the features detailed published about the SQL server 2016 by its provider.

Editions and supported features of SQL Server 2016:

You can get more concrete details about the 2016 SQL server and supported feature  at the below link :

https://docs.microsoft.com/en-us/sql/sql-server/editions-and-components-of-sql-server-2016?view=sql-server-ver15