[SAAS V15] Reconciliation number on partial payment problem following migration from V12 to V15



We recently had to update our odoo from version 12.3 to 15

We had just before the update developed a tool allowing to recover the payments reconciled towards our interface thanks to the api xmlrpc

Our goal is to be able to automatically retrieve payments through the odoo API to import them in our extranet and to assign them to customer invoices.
In version 12.3, if the payment only partially pays the invoice, it created a unique reconciliation number for us as for a full payment. But since the update to v15 of odoo, if we reconcilied a partial payment to an invoice, the "partner ledger" (not sure of the translation) only returns us: "P" instead of something like A22533.
Is it not possible to have a lettering number even for a partial payment?

Thanks in advance.