Hello
The error “RPC server is unavailable. 0x800706ba (WIN32: 1722 RPC_S_SERVER_UNAVAILABLE)” is a common error that can occur when enrolling for a certificate on a Windows Server.One possible cause of this error could be a network issue. You may want to check if the RPC ports required for certificate enrollment are already opened (TCP 135 and dynamic ports). Another possible cause could be incorrect group policy configurations, missing “NT Authority\Authenticated Users” in the “Users” group of the certificate server or any other default permissions, or missing “NT AUTHORITY\Authenticated Users” from the “Certificate Service DCOM Access” local group of the certificate server. You may want to check these settings and make sure they are configured correctly.
https://learn.microsoft.com/en-us/troubleshoot/windows-server/identity/error-0x800706ba-certificate-enrollment