Verify the WSUS installation
Windows Server Update Services (WSUS) is an optional server role that you install and enable in the Windows Server operating system. WSUS uses Microsoft Update to distribute Windows patches and hotfixes to systems in a corporate network. Patch Manager integrates with WSUS to provide the software distribution engine for pushing Windows and third party updates to the managed systems.
Enable WSUS on the Patch Manager server or a separate server in the domain. If you install WSUS on a separate server, ensure that the Patch Manager and WSUS servers are running identical Windows Server operating systems. Otherwise, you must install an Automation Server role to prevent API Mismatch errors when you publish your Windows and third-party updates.
See the Microsoft Docs website for details about deploying WSUS in a corporate environment.