I have two separate sharepoint lists. List "A" shows all invoices received to date and references a TacticID that is unique to a specific deliverable. This list has multiple invoice "Amounts" per deliverable ("TacticID").

Sharepoint list "B" has more detail related to each TacticID (i.e. deliverables and timelines) including a column for total amount of invoices received.
I am trying to sum all of the invoice "Amount" values for a given "TacticID" from "List A" to the "Total Invoice" column of the matching "TacticID" on "List B". Ideally each deliverable in "List B" would have the corresponding invoice totals showing up in the "Total Invoice" column of "List B".
I have been trying to make this happen for a couple of days now, but I have not found any good solution to it. Any help would be greatly appreciated