It’s inevitable that someone will miss important fields on your forms. To help avoid this, you should allow the form to provide users with accessible feedback.
It is important to avoid visual error and verification feedback. If your form tells users that required fields are in red, then visually impaired users will not be able to see that indication. Similarly, any error message that says the incorrect fields are highlighted will be inaccessible to those users.
Many forms do not display a submit button until specific fields are complete, but this can cause confusion for any user. Tell the users exactly what they need to do to complete the form and avoid disabling the submit button; instead, allow the user to click the submit button and reload the page, clearly telling the user where they have made errors or omitted information.