I am very surprised that turnover in France is based on payments and not on invoices.
That's against international generally accepted accounting principles (GAAP).
What you are suggesting here is a fully blown automated accounting system for VAT, which goes way beyond anything I'm aware of in the market (open-source or proprietary).
CBSubs is not an automated accounting system, and is not planed to become one (even if I would love to have it for our own business here).
Maybe by taking the bank statements, you could just have a single system for VAT reporting for all your cash flows
ok, now that generalities are said
:
Payment records do not have any VAT computations (and I am not aware of any accounting system that has that, as VAT is always linked to invoices, and actually to invoice items). Also for partial payments of multiple items with different VAT rules, the payment cannot guess what the payment is for.
So having the VAT report based on payments table instead of invoices is technically and form an accounting standpoint not an option.
Additionally, you still need documents that you can show to your VAT inspectors in case you have an inspection. And those documents are invoices and credit-notes.
The normal way accountants do account for partial payments of full invoices that are issued is by issuing manual credit notes ("Note de crédit") which contain negative VAT (or credited VAT amount corresponding to the unpaid amount). Those credit-notes are "negative invoices".
CBSubs is not a manual invoicing system, and does not support such manual credit notes, which would have to be issued by your accountant separately (e.g. with a text-processing or a spreadsheet).
Not knowing your use-case, it's hard to make an educated guess on which solution is best. Maybe a donation plan to account for the paid amounts generating a separate invoice instead of the original one could help in those few very particular case where you have partial defaults of payments. Or just account separately those partial payments with manualy issued credit-notes outside CBSubs ?