The L2TP tunnel name sent by the PC to the USG is different from the one configured on the USG, causing a failure to find a matching L2TP group.
Use either of the following methods to resolve the problem:
Change the computer name of the PC.
Change the computer name of the PC to client1.
Change the remote tunnel name on the USG.
Change allow l2tp virtual-template 1 remote client1 to allow l2tp virtual-template 1 on the USG.
You can choose to configure a remote L2TP tunnel name in the l2tp-group 1 view but must configure a remote tunnel name in other l2tp-group views.