About type is Calculated and the type of Zabbix aggregate use problem.

I create an ITEM in a host(nanjing-hof-zabbix-proxy-1:nanjing-hof-vmware-vsan-site-1)

I created a first type: Zabbix aggregate entry, as follows:
grpsum[["??-??1-???-??-HOFNJ_VSAN"],Manual-Total-Memory,last,0]

Note:"??1?-??-HOFNJ_VSAN" is a host group. Manual-Total-Memory is a ITEM.

And then I created a type of: Calculated,as follows:
last("grpsum["??-??1-???-??-HOFNJ_VSAN","Manual-Total-Memory","last"]")

In the end I see just the new ITEM, display the following error:

Cannot evaluate expression: expected numeric token at "last("grpsum["??-??1-???-??-HOFNJ_VSAN","Manual-Total-Memory","last"]"))".

How can I solve this error?