You can retrieve your production and sandbox API keys from the API keys page.

All requests must be made over HTTPS and will be authenticated over standard OAuth authentication. When providing credentials, the username will be your Client ID and the password will be your Client Secret.

API keys must be kept secret. They should not be in your client-side code or checked into your application's code.

Sandbox

POST oauth2/token HTTP/1.1
Host: auth-sandbox.prod.swifterhq.com
 
grant_type=client_credentials
&audience=sparc-pay
&client_id=xxxxxxxxxx
&client_secret=xxxxxxxxxx

Live

POST oauth2/token HTTP/1.1
Host: sparc-pay-auth.prod.swifterhq.com

grant_type=client_credentials
&audience=sparc-pay
&client_id=xxxxxxxxxx
&client_secret=xxxxxxxxxx