Free delivery is not free. You pay the courier either way; the only question is whether the cost is visible to the buyer or buried in your price.
So the real question is which of those sells more, and the answer differs by what you sell.
The version that works: a threshold
Set delivery free above an amount, and the checkout says so — Free above ₹{amount}.
That does three things at once: it raises the size of an average order, it rewards the buyer for combining, and it means you are only absorbing the cost on orders big enough to carry it.
It is the one form of free delivery that is reliably worth doing. How to set delivery prices
Where to set the threshold
Above your current average order, not at it. If people usually spend ₹600, a threshold at ₹900 moves behaviour. One at ₹500 just gives away the postage you were already charging.
Look at your own numbers rather than copying someone else's. How to find your store's numbers
Where flat free delivery does make sense
Small, light, uniform things. If everything you sell posts for the same small amount, folding it into the price is simpler for everyone and costs you nothing in accuracy.
A deliberate promotion, for a week, to see what happens.
Where it goes badly wrong
A mixed range. If you sell earrings and lampshades, one price that covers the lampshade overcharges every earring buyer, and one that suits the earrings loses money on every lampshade. That is not a pricing problem, it is a missing second delivery option. What is a delivery profile?
Anything bulky. Couriers charge for space, so a light large parcel costs far more than the scale suggests — and free delivery on those is a slow leak you may not notice for a month. Why does a big light box cost so much to send?
Across a whole country. Metro to metro and remote PIN codes are not the same price, and a flat free rate quietly means you lose most on the orders furthest away.
The commission angle, which cuts the other way
Metzee's commission is worked out on the item, not on the delivery. So burying delivery in the item price means paying commission on the postage. Charging it separately does not. Is commission charged on the delivery I collect?
That is a real reason to show delivery as delivery.
What buyers actually respond to
Not the word free so much as not being surprised. A clearly stated ₹60 at checkout loses fewer carts than a vague one, and far fewer than a delivery cost that appears late.
Pickup, where you can offer it, beats both. What is a pickup point?
More: how delivery is charged, how do I work out what to charge for postage, how to set delivery zones.