If you make 3 invoices to the same client for $1,000 each plus VAT and the client pays you $2,400 in a single deposit and you want to apply the payment of $800 to each invoice from that advance of $2,400. How do you apply a fraction to each invoice from a single deposit and that the payment generates the correct payment complement to the SAT (Mexican Authorities)  comes out for $2,400 relating the 3 invoices and showing an equal balance payable in the 3 invoices?

Try it with a batch payment, first pay the $800 to each invoice, indicating that it was a batch payment with your payment method to funds transfer. Then create the batch payment of $2,400 and match the 3 paid invoices to their $800 each. The system allowed me to reconcile the bank statement for $2,400 and the payment was perfectly applied, but it made me 3 payment complements to SAT, one for each payment, and that is fiscally wrong. It should be a single payment complement for $2,400 relating to the 3 CFDI and indicating the outstanding balance of each invoice and the partiality payment number.

As I understand after reading all the documentation and doing a lot of tests, it is not possible with Odoo in its standard version, it is an issue that many clients have with Odoo in Mexico. 

Currently, it pays the oldest bills first and applies the entire amount, which results (residual) being applied successively to the next one. The need is to be able to apply the desired amount of that advance to the invoice and not the total, but that the payment complement to the SAT is unique as indicated in accordance with Mexican legislation.

Does someone know some app that gives us the opportunity to edit the advance payment for each invoice before the application? some idea?

Thanks and best regards!!!