Can I pass on supplier's GST bill to my client without adding my own GST

Hi Tax experts,

I have a question regarding GST invoice that I send to my clients. I buy digital advertisement from Facebook for my client. Facebook's Invoice is on my GSTIN and already has 18% GST on it.  When I pass on this bill to my client I add my charges too onto it which I do add GST. When I send the total invoice to my client, should I add another 18% on Facebook's invoice ? 

  Example is as below:

       1. Facebook ads cost which I bought for my client = Rs.1000 + GST(18%) =  Rs.1180. This GST is on my GSTIN since I bought the ads on behalf of my client.

       2. My charges for managing Facebook Ads for my client:  Rs.100.

When I invoice my client, it is obvious that I will add GST on my charges of Rs.100. My question is: should I add GST on Facebook's invoice which already contains GST ?

Thanks in advance for your insightful answers..

Regards,