Showing alert on validation of form submission
Here is our approach to showing alert on validation of form submission

Our Assumption
1. We assume that you have all mandatory fields ( Email ) to check CRM entry
2. Also you have enough API calls in the subscription
Approach
We've given the steps to showing alert on validation of form submission
1. Create workflow on form validation
1.1 Go to Workflow section and tap on "New Workflow"

1.2 Give conditions for workflow as mentioned in the below image and tap on "Create Workflow"

2.3 Tap on "Add New Action"

2.4 Choose "Deluge Script" as Action Type

2.5 Copy and paste the below code in the Code Snippet and tap on "Save"

Code Snippet
Related Community Question
Validate of Form Submission Workflow not Running on Create | Link
I have one workflow for validating a form that runs when editing or creating and works properly. However, for all new forms I cannot get the validation to run when creating. I created a new app with a simple User form and the attached workflow. It runs when editing but not creating a user. Similarly, if I create a workflow that should run only on creation it does not run either. Any idea why this would happen?

