Foundry supports collection types in request for JSON service. Collections type can mapped to application requests using Velocity templates. Refer doc Collection Support - HCL Volt MX Documentation V9.5.
From Foundry V9.5.17.4 velocity core engine 2.0 is used for processing velocity templates. There are updates and removal of velocity template language syntax in velocity 2.0 version. Below are few major once which could have impact on existing templates.
• the hypen ( - ) cannot be used in variable names anymore
• the #foreach predefined references $velocityCount and $velocityHasNext have been removed. Use $foreach.count (1-based), $foreach.index (0-based) and foreach.hasNext().
Perform updates to existing templates if any of the deprecated syntax is being used.
For more information on migration to velocity template 2.0 refer Apache Velocity Engine - Upgrading