No Coupon Code Option in Checkout

Originally there wasn’t a coupon code section showing in the checkout at all, so I added it myself. Now everytime a customer puts in his/her address, name etc and then at the coupon code all the information disappears and the customer needs to start from the beginning.

Does anyone know why that happens?

I already asked that the WooCommerce Customer support, but they said it usually is a theme issue.

For the reference – I followed this tutorial: https://monalieblog.wordpress.com/2016/08/05/add-coupon-field-in-woocommerce-checkout/

Thanks in advance

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