too long

i got this error when i try to test method in my controller

 GuzzleHttp\Exception\ClientException: Client error: `POST https://api.mailgun.net/v3/sandbox22f99fb37d4a4953a7b8d84cf89d1147.mailgun.org/messages.mime` 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...)

This is the sandbox domain. You need to verify your own domain or verify the recipient in order to send an email to others.They are for test, not for API implementation

Read more : https://documentation.mailgun.com/faqs.html#how-do-i-pick-a-domain-name-for-my-mailgun-account

Follow the link to add recipients: https://mailgun.com/app/testing/recipients