This error message is from Applea and means DEP is not available in your country.
Currently, DEP is available in the following countries/regions:
Australia, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Hong Kong, Ireland, Italy, Japan, Luxembourg, Mexico, Netherlands, New Zealand, Norway, Singapore, Spain, Sweden, Switzerland, Taiwan, Turkey, United Arab Emirates, United Kingdom, and United States.
If you want to enroll the iOS device, you must first set up the Apple Push Notification Service (APNS) certification. To do so, from the Samsung SDS IAM & EMM Admin Console, go to Settings > APNS Certificate. After you set up the APNS certification, try to enroll the iOS device.