Gst applicability for place of supply

Sagnik Majumder (Accounts Executive) (51 Points)

31 January 2020  
we have a store at kolkata. we are providing event & promotional service to other companies at our store. Now one of the delhi based company who is registered in Delhi has taken a promotional service at our kolkata store.
Kindly help either we charge cgst & sgst or Igst during Invoice.
also mention the section regarding this matter.