How can I implement validation messages in Formik?

How can I implement validation messages in Formik?

You can use the validate prop in Formik to define your validation logic and return error messages.

Can you show me an example of how to do that?

Sure! Here's a simple example:

<Formik
  initialValues={{ email: '' }}
  validate={values => {
    const errors = {};
    if (!values.email) {
      errors.email = 'Required';
    } else if (!/\S+@\S+\.\S+/.test(values.email)) {
      errors.email = 'Invalid email address';
    }
    return errors;
  }}
>
  {({ errors, touched }) => (
    <Form>
      <Field name="email" />
      {errors.email && touched.email && <div>{errors.email}</div>}
      <button type="submit">Submit</button>
    </Form>
  )}
</Formik>

What if I want to customize the error messages?

You can customize the error messages by modifying the strings returned in the errors object based on your validation logic.