Add up only paid invoices by client in Apple Numbers (14.1)

Hi all,

I'm a complete noob to Numbers and formulas, please be gentle!

This thread was close to what I want but not quite...

How to SUM only checked checkboxes in a c… - Apple Community

I'm trying to create a table that shows total paid invoice amounts by client.

In my first table "Invoices":

Column A is my Checkbox (Paid), checked if the invoice has been paid.

Column C is the client name (Client).

Column E is the Invoice Amount.

My new table is just 2 columns

Column A is the client name

Column B should be the total amount of PAID invoices only for each client.

The latest formula I've tried is this:

SUMIF(Paid,TRUE,Invoices::Invoice Amount)

This just gives me a total of everything in Column E

Prior to that I tried this:

SUMIF(Paid,TRUE,Invoices::Client,Invoices::Invoice Amount)

This just gives me the error "SUMIF requires between 2 and 3 arguments, but was given 4."

I also tried this:

Paid+TRUE+SUMIF(Invoices::Client,$A3,Invoices::Invoice Amount)

I get a warning with the message "The formula uses a Boolean in place of a number." but it does give me a total however it also disregards whether Paid has been checked.

Am I close with any of these? I'm guessing I need to say what should happen if Column A isn't checked?

Any help much appreciated!