You are trying to associate Exchange policy to Android devices and get an error "Unable to configure Exchange policy"
This error occurs due to one of the following reasons:
The device must be passcode-protected to associate Exchange policy. You can configure and distribute a passcode policy to Android devices as explained here.
The certificate used to configure Exchange policy might be corrupt. Verify if the certificate can be manually installed on the device
Verify if the account credentials are valid by manually configuring the policy
If the mail client on the device is Microsoft Outlook or Gmail, update them to the latest version and try again.
If the issue persists, contact MDM support with Server logs as explained here.