Short answer. No, that payment is not valid. Article 1243 provides that once a court has judicially ordered you, as debtor, to retain the debt, any payment you then make to the creditor is void. You remain obligated to hold the funds for whoever the court's order protects.
What the law says
Payment made to the creditor by the debtor after the latter has been judicially ordered to retain the debt shall not be valid.
Civil Code, Article 1243 — Payment After Garnishment. Read the full provision →
What it means to be ordered to retain a debt
You can end up bound by an order to retain a debt when someone else has a claim against your own creditor, and a court directs you, as the person who owes that creditor money, to hold on to the funds instead of handing them over. The order effectively freezes the debt in your hands so it can be reached to satisfy the other claim. From the moment that order reaches you, your ordinary freedom to simply pay your creditor whenever the debt falls due is suspended by court authority, not by anything your creditor did.
Paying anyway does not settle your obligation
Article 1243 is direct about the consequence of ignoring such an order: payment made to the creditor by the debtor after the latter has been judicially ordered to retain the debt shall not be valid. A payment that is not valid does not extinguish your obligation. In the eyes of the law, it is as though you never paid at all, even though the money has already left your hands and gone to the creditor.
Why this exposes you to paying twice
Because an invalid payment does not discharge the debt, you can end up having to pay the same amount a second time, this time to whoever the retention order was meant to protect. Handing money to your creditor after being told to retain it does not shift the loss onto that other party; it simply means you parted with funds that the law says you should not have released. Whether you can later recover what you mistakenly paid from your creditor is a separate question from whether your underlying debt is considered paid, and the two should not be confused.
What to do once you receive such an order
If a court has directed you to retain a debt you owe, the safest course is to stop making any payment on that debt to your original creditor until the order is lifted or the matter is otherwise resolved. Continuing to pay as though nothing happened does not protect you; it only adds a second obligation on top of the one you already have. If you are uncertain whether an order actually applies to your situation, or how long the retention is meant to last, that uncertainty should be resolved before any further payment is made, not after.