Is the oil suitable under nail polish or gel polish? — DNC Walnut oil barn strengthening 6ml

The card speaks neither of using the oil under polish or gel polish nor of combining it with coatings. The recommendation is one: apply a small amount to the nails and cuticles, preferably at night.

General information (not a manufacturer's instruction): a layer of oil can reduce the adhesion of the coating to the nail, so it is usually removed before polishing; ask your nail technician.