Gst on expenses apportionment debit note

We have got two Pvt Ltd viz. A and B .One is cumming under GST preview and it is registered under GST  ie. A. I want to share some of the common expense with B company by raising Debit Note. We are the service providers and not having any trading activity. Should I charge GST on the Debit Note raised by A company to B company. Pls explain.