ok, I got this excerpt from
www.greenscapular.com I think it answers your question
Sister suffered much during this time. Finally, after a thorough investigation and careful discernment, the local Bishop approved the apparitions and was ready to permit the spread of this new sacramental. Our Lady, however, had never been clear about certain aspects of this new devotion. Questions needed to be answered. What circumstances were necessary to make the scapular effective? Was there a special blessing for it? Was there a ceremony for enrolling persons in its use? Were there any obligations for those who used it? Was the scapular for use only by certain groups of people or in certain situations?
To resolve these difficulties it was decided that Sister Justine would ask Our Lady herself what God’s Holy Will was in these matters. Our Blessed Mother replied during an apparition on September 8, 1846 - exactly six years after her initial request for this “Badge of the Immaculate Heart”.
Our Lady replied: This scapular is not like others (it is not the clothing-habit of a confraternity) but merely two holy pictures on a single piece of material. Therefore no special formula is required to bless it or enroll someone in its use. It suffices that it be blessed by a priest and worn by the one whom we desire to benefit by Our Lady’s intercession. If, on the other hand, the person is unable or even unwilling to wear it or carry it, it may even be slipped, unknown to him, into his clothes, bed, room, or possessions etc.
There is only one prayer that needs to be said, at least once a day: “Immaculate heart of Mary, pray for us now and at the hour of our death.” If the person who is the intended beneficiary of the scapular’s use does not say it, then someone else can say it in his place. The Green Scapular may be used anywhere, for anyone. The greatest graces are attached to its use, but these graces are more or less great in proportion to the degree of confidence of the person praying. This was the meaning of the different kinds of rays that fell from the Mother of God’s hands at the last apparition.
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