Hi Patrick,
Thanks for contacting Syncfusion Support.
Currently, we don’t having a support for stop the report rendering based on the parameter validation using custom code. However, we can achieve this by using “Visibility” of report items. To achieve this follow the below steps.
1) add a textbox to the report that is visible only if validation fails. This text box you can use to display an error message to the user.
2) put the rest of your report in a rectangle and set it to be hidden if there is a parameter validation error. So the report will not render in report viewer if there is validation error.
We have prepared a sample report based on this and it can be downloaded from the following location.
Regards,
Vinoth S.