original_string: public function refreshAccessToken($refreshToken, $expiresIn = null)
      {
          $parameters = [
              'grant_type' => 'refresh_token',
              'refresh_token' => $refreshToken,
          ];
  
          if ($expiresIn != null) {
              $parameters['expires_in'] = $expiresIn;
          }
  
          return $this->tokenRequest('oauth2/token', $parameters);
      }
code: public function refreshAccessToken($refreshToken, $expiresIn = null)
      {
          $parameters = [
              'grant_type' => 'refresh_token',
              'refresh_token' => $refreshToken,
          ];
  
          if ($expiresIn != null) {
              $parameters['expires_in'] = $expiresIn;
          }
  
          return $this->tokenRequest('oauth2/token', $parameters);
      }
code_tokens: public function refreshAccessToken ( $ refreshToken , $ expiresIn = null ) { $ parameters = [ 'grant_type' => 'refresh_token' , 'refresh_token' => $ refreshToken , ] ; if ( $ expiresIn != null ) { $ parameters [ 'expires_in' ] = $ expiresIn ; } return $ this -> tokenRequest ( 'oauth2/token' , $ parameters ) ; }
docstring: Refresh Fitbit token.
  
  @param string $refreshToken refresh token
  @param int|null $expiresIn set length of token
  @return ResponseInterface response from Fitbit API
docstring_tokens: Refresh Fitbit token .