Whether GST is applicable on interest charged by Del credere Agent

In Re M/s Shreenath Polyplast Pvt Ltd (AAR Gujarat) We know that as per section 15(2)(4) of CGST ACT  GST is applicable on interest or penalty levied by the seller on buyer on account of delay in payment of consideration of supply. So if Mr X supplied goods worth Rs 10,000 (including GST @ 18%) to Mr Y on 01.01.2018 with the condition that Mr Y need to make payment by 31.01.2018 else interest will be applicable.  In this case if Mr Y actually made payment of Rs 10,000 on 31.03.2018 and as a result of delay in payment Mr X levies interest of Rs 200 (say) then Mr X is required to pay GST @ 18%...