TDS Deduction

Dear experts,

please suggest me

we are booking air ticket through agent for employee after that he raise invoice our company name.
bill contain service charge & air ticket amount .he charge get only service amount.
for exp.

service charge. 500
gst 18%. 90
air ticket bill amt 1000

total bill amount. 1590.

my question is that which amount I have deduct TDS. 1500 or only 500 .