Tagging Valid and Invalid Data/Paths
In Test Modeller, you can add tags to Action blocks to identify paths as having Valid data (happy path) and Invalid data (unhappy path). The tag is then displayed in the test case menu, specifying whether the path is happy/valid or unhappy/invalid:

You can furthermore filter Valid and Invalid generated paths, following the instructions in this article.
There are two ways to mark an Action Block.
Method 1
Select the Action Block
Click on the Properties button from the button list on the right of the window
Click in the Data Type dropdown and select one of the options

Method 2
Right-click on the Action Block
click on the Data Type option to display the sub-options
Select the required tag

TEST MODELLER TEST CASE GENERATION