¿Qué significa When we have the gender in the envelope, I will bring it to the store so they can wrap the correct outfit ?

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A couple is having a baby, but the gender is a secret. Someone is going to pre-pay for a onesie (one-piece baby outfit) for the baby as a gift. Blue if the baby is a boy, pink if the baby is a girl. The person doesn't know the gender of the baby since it's a secret.
The couple will put the gender in the envelope so the person buying the gift can't see it. It will say boy or girl or maybe they'll put a piece of pink or blue paper in the envelope. The person buying the gift will take the envelope (unopened) to the store. The store clerk will open the envelope, see what the gender of the baby is, and wrap the blue onesie if the baby is a boy or the pink onesie if the baby is a girl. The person buying the gift won't see if it's blue or pink since it's supposed to be a surprise/secret.