code: func (c *Client) GetDomainID(domainName string) (string, error) {
  	domainList := &DomainListResponse{}
  
  	err := c.do(http.MethodGet, "/v1/domains", nil, domainList)
  	if err != nil {
  		return "", err
  	}
  
  	for _, domain := range domainList.Domains {
  		if domain.Name == domainName {
  			return domain.ID, nil
  		}
  	}
  	return "", fmt.Errorf("no such domain: %s", domainName)
  }
docs: // GetDomainID returns an ID of specified domain.