Zoho CRM Reports Aggregate Column Sum Missing

Zoho CRM Reports Aggregate Column Sum Missing

Hello,

In two out of three custom modules in our organization's CRM, the aggregate column for reporting does not show the "sum" feature (image below). I'm not sure what the case, but the reports are generated the same way in that there are no other parents/children associated with them and they are simply text input fields.

Any idea what I am missing?