If you wish to use the Exotel APIs, you will need to authenticate yourself. <your_api_key>, <your_api_token> and <your_sid> will help you do that. These details will be available in the API settings page.
By default your account belongs to Singapore cluster . So use the subdomain of Singapore cluster. If your account is created in Mumbai cluster, use the subdomain of Mumbai cluster.
<subdomain> of Singapore cluster is api.exotel.com (If the Exotel Account URL is my.exotel.com then use this subdomain)
<subdomain> of Mumbai cluster is api.in.exotel.com (If the Exotel Account URL is my.in.exotel.com then use this subdomain)
API settings Page: