code: func (p *Pushover) GetRecipientDetails(recipient *Recipient) (*RecipientDetails, error) {
  	endpoint := fmt.Sprintf("%s/users/validate.json", APIEndpoint)
  
  	// Validate pushover
  	if err := p.validate(); err != nil {
  		return nil, err
  	}
  
  	// Validate recipient
  	if err := recipient.validate(); err != nil {
  		return nil, err
  	}
  
  	req, err := newURLEncodedRequest("POST", endpoint,
  		map[string]string{"token": p.token, "user": recipient.token})
  	if err != nil {
  		return nil, err
  	}
  
  	var response RecipientDetails
  	if err := do(req, &response, false); err != nil {
  		return nil, err
  	}
  
  	return &response, nil
  }
docs: // GetRecipientDetails allows to check if a recipient exists, if it's a group
  // and the devices associated to this recipient. It returns an
  // ErrInvalidRecipient if the recipient is not valid in the Pushover API.