Conditional Validation in Yup

You probably aren’t defining a validation rule for the showEmail field.

I’ve done a CodeSandox to test it out and as soon as I added:

showEmail: yup.boolean()

The form started validation correctly and no error was thrown.

This is the url: https://codesandbox.io/s/74z4px0k8q

And for future this was the correct validation schema:

validationSchema={yup.object().shape({
    showEmail: yup.boolean(),
    email: yup
      .string()
      .email()
      .when("showEmail", {
        is: true,
        then: yup.string().required("Must enter email address")
      })
  })
}