How to get the index of the link to another table

[wengestionrr]

Let's say I have a table of Invoices and then a table of payments. Each invoice is an aggregate of payments i.e. one invoice can have multiple payments. How can I get the index of each payment in the list of the invoice?

[Alexey_Gusev]

Hi,
a short example
Invoices:

Payments (here, in example, first letter is Invoice name)

Copying field INV to link field:

Created links auto-create back links in other table:

Which can be accompanied by lookup field(s)

and ROLLUPS:

I hope this example will help you.