REQUEST: POST - https://desk.zoho.com/api/v1/tickets 
{
   "subject":"testing_email_validation",
   "contact":{
      "email":"testing_symbol_!_@test.com"
   },
   "departmentId":"550547000008403071"
} 

RESPONSE: 422 
{"errorCode":"INVALID_DATA","message":"The data is invalid due to validation restrictions","errors":[{"fieldName":"/email","errorType":"invalid","errorMessage":""}]}

If I remove "!" - everything is ok.
How I must escape symbol "!" in the email. Where can I find validation rules for email in zoho desk api?

P.S.:
- I'm use php curl (guzzle) for api
- url encode does not help
- \ (back slash) does not help
- no custom validation rules in the zoho desk admin