How to reject sign-up trigger with GoLang - amazon-web-services

Question

I've successfully created a lambda function using Go for the pre sign-up trigger of AWS Cognito.
My problem is that I'm not being able to deny/reject the user if a custom field is not valid (based on custom logic).
I'm returning an error as described in AWS Cognito trigger's guide:
return event, fmt.Errorf("Invalid value for field 'custom:myField'")
also I've tried this options:
returning an empty event (nil is not allowed for the event):
var emptyEvent events.CognitoEventUserPoolsPreSignup
return emptyEvent, fmt.Errorf("Invalid value for field 'custom:myField'")
changing ValidationData in the original event:
event.Request.ValidationData = map[string]string{"custom:myField": "Invalid value for field 'custom:myField."}
return event, fmt.Errorf("Invalid value for field 'custom:myField'")
changing UserAttributes in the original event
event.Request.UserAttributes["email"] = ""
return event, fmt.Errorf("Invalid value for field 'custom:myField'")
All those methods are failing, the user is always created in the User Pool.
What should be the correct way to reject the sign-up request using GoLang lambda function?

Answer 1

Looks like something changed on AWS Cognito Lambda triggers, since today I tried the following source code and it worked as expected:
func handler(event events.CognitoEventUserPoolsPreSignup) (events.CognitoEventUserPoolsPreSignup, error) {
fmt.Println(event)
return event, fmt.Errorf("TESTING LAMBDA ERRORS WITH GOLANG")
}
Also, the previous source code that was not working as expected when I posted this question is currently working (with no changes on my side).