When using the Stayman convention after your partner opens 1NT (or a 1NT overcall), only use it if you have at least one 4-card major suit. The purpose of Stayman is to explore whether your partner also holds a 4-card major, aiming for a better major suit fit. If you lack a 4-card major, consider other bids like a direct raise or a transfer, depending on your hand's strength and distribution.
