Trying to test out the community self-registration with the registration page type of "configurable self-reg page", but I upon clicking register with my phone number I am returned a "Can't verify phone number. For help, contact your community manager." error.

The login page type is set to default page.

I am including the Last Name, First Name, and Mobile fields.

I am using the automated "create a configurable self-reg handler" function to create my apex handler class, and I have viewed the class and everything is as expected.

I have set the "execute registration as" user as myself which is a system admin profile.

Verification method is set to "Text Message".

For the "assign users to a profile and account" page, I have selected the customer community user profile.

If I manually type this phone number into the user object via setup, it takes it. Ex: 3131234567.

Configurable Handler Registration Class (Auto-created):

global class AutocreatedConfigSelfReg1542644056573 implements Auth.ConfigurableSelfRegHandler {

  private final Long CURRENT_TIME = Datetime.now().getTime();
  private final String[] UPPERCASE_CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
  private final String[] LOWERCASE_CHARS = 'abcdefghijklmnopqrstuvwxyz'.split('');
  private final String[] NUMBER_CHARS = '1234567890'.split('');
  private final String[] SPECIAL_CHARS = '!#$%-_=+<>'.split('');

  // This method is called once after verification (if any was configured)
  // This method should create a user and insert it
  // Password can be null
  // Return null or throw an exception to fail creation
  global Id createUser(Id accountId, Id profileId, Map<SObjectField, String> registrationAttributes, String password) {
    User u = new User();
    u.ProfileId = profileId;
    for (SObjectField field : registrationAttributes.keySet()) {
      String value = registrationAttributes.get(field);
      u.put(field, value);
    }

    u = handleUnsetRequiredFields(u);
    generateContact(u, accountId);
    if (String.isBlank(password)) {
      password = generateRandomPassword();
    }
    Site.validatePassword(u, password, password);
    if (u.contactId == null) {
      return Site.createExternalUser(u, accountId, password);
    }
    u.languagelocalekey = UserInfo.getLocale();
    u.localesidkey = UserInfo.getLocale();
    u.emailEncodingKey = 'UTF-8';
    u.timeZoneSidKey = UserInfo.getTimezone().getID();
    insert u;
    System.setPassword(u.Id, password);
    return u.id;
  }

  // Method to autogenerate a password if one was not passed in
  // By setting a password for a user, we won't send a welcome email to set the password
  private String generateRandomPassword() {
    String[] characters = new List<String>(UPPERCASE_CHARS);
    characters.addAll(LOWERCASE_CHARS);
    characters.addAll(NUMBER_CHARS);
    characters.addAll(SPECIAL_CHARS);
    String newPassword = '';
    Boolean needsUpper = true, needsLower = true, needsNumber = true, needsSpecial = true;
    while (newPassword.length() < 50) {
      Integer randomInt = generateRandomInt(characters.size());
      String c = characters[randomInt];
      if (needsUpper && c.isAllUpperCase()) {
        needsUpper = false;
      } else if (needsLower && c.isAllLowerCase()) {
        needsLower = false;
      } else if (needsNumber && c.isNumeric()) {
        needsNumber = false;
      } else if (needsSpecial && !c.isAlphanumeric()) {
        needsSpecial = false;
      }
      newPassword += c; 
    }
    newPassword = addMissingPasswordRequirements(newPassword, needsLower, needsUpper, needsNumber, needsSpecial);
    return newPassword;
  }

  private String addMissingPasswordRequirements(String password, Boolean addLowerCase, Boolean addUpperCase, Boolean addNumber, Boolean addSpecial) {
    if (addLowerCase) {
      password += LOWERCASE_CHARS[generateRandomInt(LOWERCASE_CHARS.size())];
    }
    if (addUpperCase) {
      password += UPPERCASE_CHARS[generateRandomInt(UPPERCASE_CHARS.size())];
    }
    if (addNumber) {
      password += NUMBER_CHARS[generateRandomInt(NUMBER_CHARS.size())];
    }
    if (addSpecial) {
      password += SPECIAL_CHARS[generateRandomInt(SPECIAL_CHARS.size())];
    }
    return password;
  }

  // Generates a random number from 0 up to, but not including, max.
  private Integer generateRandomInt(Integer max) {
    return Math.mod(Math.abs(Crypto.getRandomInteger()), max);
  }

  // Loops over required fields that were not passed in to set to some default value
  private User handleUnsetRequiredFields(User u) {
    if (String.isBlank(u.LastName)){
      u.LastName = generateLastName();
    }
    if (String.isBlank(u.Username)) {
      u.Username = generateUsername();
    }
    if (String.isBlank(u.Email)) {
      u.Email = generateEmail();
    }
    if (String.isBlank(u.Alias)) {
      u.Alias = generateAlias();
    }
    if (String.isBlank(u.CommunityNickname)) {
      u.CommunityNickname = generateCommunityNickname();
    }
    return u;
  }

  // Method to construct a contact for a user
  private void generateContact(User u, Id accountId) {
    // Add logic here if you want to build your own contact for the user
  }

  // Default implementation to try to provide uniqueness
  private String generateAlias() {
    String timeString = String.valueOf(CURRENT_TIME);
    return timeString.substring(timeString.length() - 8);
  }

  // Default implementation to try to provide uniqueness
  private String generateLastName() {
    return 'ExternalUser' + CURRENT_TIME;
  }

  // Default implementation to try to provide uniqueness
  private String generateUsername() {
    return 'externaluser' + CURRENT_TIME + '@company.com';
  }

  // Default implementation to try to provide uniqueness
  private String generateEmail() {
    return 'externaluser' + CURRENT_TIME + '@company.com';
  }

  // Default implementation to try to provide uniqueness
  private String generateCommunityNickname() {
    return 'ExternalUser' + CURRENT_TIME;
  }
}

Any idea on what would could case the phone number verification to fail?