In order to create your free shipping coupon code. Follow the below steps
On the Mayzing Dashboard, click on promotions, then store promotions.
Click on create promotion.
Give your promotion a name, something to help you identify it later. Something like Coupon Code.

Click Free shipping in region.

Choose the region or regions you would like to offer free shipping in.

If you want to add a minimum cart value, you can in the next section.

Now under discount method. Select Coupon code.

Choose your coupon code. In this example we’ll call it FREESHIP.

Press create discount.
Publish your store.
Now you can send your coupon code to your selected audience. When they get to the cart and add the coupon code. It will give them free shipping.

It is worth noting that they may be on priority shipping which has a surcharge. If they change that back to standard shipping, the shipping will be zero.