You no need add RAM to VM.
Connect SSH to vCenter Server Appliance, enter bash command "shell".
List current service RAM set (save before edit):
cloudvm-ram-size -l
View memory usage statistic:
cloudvm-ram-size -S
If value in "CurrentMB" above "AllocatedMB" - may, but not neccesary, need up service set.
Worked for me to solve problem in default VCSA installation:
cloudvm-ram-size -C 1024 vmware-vpostgres
service-control --stop vmware-vpostgres;service-control --start vmware-vpostgres;
cloudvm-ram-size -C 2048 vsphere-ui
service-control --stop vsphere-ui;service-control --start vsphere-ui;
Refresh Health status on vCenter Server Manager page.