Is this oral loan agreement legally valid?

Answer

The key article to answer your question is Article 1134 of the Civil Code. This reads as follows:

“All agreements entered into lawfully shall be lawful to those who entered into them.
They cannot be revoked except with their mutual consent or on the grounds recognized by law.
They must be executed in good faith.”

It follows from this that every agreement, insofar as it is not illegal (eg drug trafficking, carrying out a construction crime,…), will be complied with. The oral nature of your agreement therefore has no consequences for its validity.

However, the verbal nature of your agreement can cause problems in terms of evidence. Your bank statements can serve as the beginning of proof of the sums at stake, and the unprotested registered notices can be invoked against a merchant as the beginning of proof that there is indeed a loan that is not being paid off, but in a any lawsuit it will be up to the judge to decide to what extent and for what he accepts all this as evidence.

If it concerns relatively large sums of money, it is best to contact a lawyer. He or she can advise you on procedural options and also conduct a possible procedure for you. Keep in mind that litigating costs money and lawyers also charge a fee. In the case of small sums and/or a presumably insolvent counterparty, it is often wiser to simply accept your loss instead of incurring further costs.