Use this request to opt in a phone number that is opted out, which enables you to resume sending SMS messages to the number.
You can opt in a phone number only once every 30 days.
/// Indicates that the user has been denied access to the requested resource.
///
/// Indicates an internal service error.
///
/// Indicates that a request parameter does not comply with the associated constraints.
///
/// Indicates that the rate at which requests have been submitted for this action exceeds
/// the limit for your account.
///
