To verify consistency of your diagram, right-click the canvas and click Validate diagram on the context menu.
If your diagram is validated successfully, the following notification appears:
If a validation problem was found, the Problems view displays an error or warning. The element that caused the error is marked on the diagram with a red cross icon, so you can easily find and fix it. Refer to the ISP validation messages or APEX2 validation messages topic for recommended action for resolving the error.
Once the error has been fixed, validate your diagram again to remove the error mark.