Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authoriz

I got this error

GuzzleHttp\Exception\ClientException: Client error: `POST http://ift.tt/2riapfS` resulted in a `400 BAD REQUEST` response:
{
  "message": "Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authoriz (truncated...)

when i trying unit test for function i have ? how i can fix that ??

via Chebli Mohamed