Magento2 implements CyberSource Secure Acceptance Method and you must configure CyberSource with Profile ID, Merchant ID, Transaction Key, Access Key and Secret Key.
I have tested CyberSource with our sandbox account and it's work as expected.
Please ask merchant try to follow next steps: Goto sandbox account https://ebctest.cybersource.com
Tools & Settings -> Profiles -> Select your profile
Press Open Editable Version -> Customer Response Pages and enter URL like https://your-host.com/cybersource/SilentOrder/TokenResponse
Press Save
Press Promote to Active
After that go to Magento Admin Panel -> Stores -> Configuration -> Sales -> Payment Methods -> Cybersource
You must enter Profile ID, Merchant ID, Transaction Key, Access Key, Secret Key, Test Mode [Yes] (If you are using sandbox account)
If you don't have these values please contact with support CyberSource to get it.