Following retainer invoice for partial payment of a sales order

Following retainer invoice for partial payment of a sales order

HI,

We issue sales orders when a client buy a product from us. We also issue multiple retainer invoices for partial payment (2 to 4 depending of the client).
Team wants to follow payment of these retainer invoices for this Sales Order. If they are paid or not.

They suggest to have a box like with invoices, displaying which invoices have been issued).

I couldn't find a way to "attach" a retainer invoice to sales order line invoice.

What would be the best way to do it ? or get around it ?

Thank you !