SQL Server Express is installed by the Cisco Unified Attendant Server installer if an existing installation
of SQL Server is not detected. Are you using resiliency or any reason you don't want SQL to be installed by CUAC.
I would try if the default install works also if you do require a more advance sql version than express I would try to do SQL Server 2016 not SQL Server 2016 SP2 and see what results you get. SQL Server 2016 SP2 is not officially listed in release notes.
https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/cucmac/cuaca/12_0_4/release_notes/CUACA_RN_12042001.pdf
Server Operating Systems
The following versions are supported:
– Windows Server 2012 R2 (64-bit)
– Windows Server 2016 (64-bit)
Requirements
• Windows server regional settings must be set to English.
• High Availability installations require that the date and time zone of the publisher and subscriber
servers match.
• Cisco Unified Attendant Console Advanced server must be installed and operated exclusively on a
supported platform.
• Server cannot be configured as a domain controller.
SQL Server Support
The following versions are supported:
– SQL Server 2012, 2014, 2016
Note SQL Server Express is installed by the Cisco Unified Attendant Server installer if an existing installation
of SQL Server is not detected.
Requirements
• High Availability Installations require SQL Server Standard or Enterprise.
• Off-box SQL installations are not supported.
• Named instances are not supported.
• Cisco Unified Attendant Console Advanced requires exclusive use of SQL Server.
• SQL login used at installation and in production requires sysadmin role association.
Also the design guide for reference
https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/cucmac/cuaca/12_0_4/design_guides/CUACA_DG_120401.pdf
