Hi,
When I try to add the coupon to my cart, I get this error:
i.imgur.com/VkodEtO.png
So I was still not able to look at problem 1.
Regarding problem 2, I can see that the problem is that you're using the code from the cart module for the delete button in the context of the checkout.
I can this code:
<a href="/سبد-خـرید-دوره-ها/product/updatecart/cart_product_id-96242/quantity-0?cart_id=92609&return_url=L9iz2KjYry3YrtmA2LHbjNivLdiv2YjYsdmHLdmH2KcvY2hlY2tvdXQ%3D" data-cart-id="92609" data-cart-type="cart" data-cart-product-id="96242" onclick="if(window.hikashop) { return window.hikashop.deleteFromCart(this, null, 'hikashop_cart_650'); }" title="حذف">
<svg version="1.0" xmlns="http://www.w3.org/2000/svg" width="256.000000pt" height="256.000000pt" viewBox="0 0 256.000000 256.000000" preserveAspectRatio="xMidYMid meet">
.... svg data .....
</svg>
</a>
As you can see, you have a call to window.hikashop.deleteFromCart. This call is actually the same you have in the cart module.
The problem is that "this" is a reference to the button clicked (in the checkout when you click on it in the cart view of the checkout), and hikashop_cart_650 is the id of the div encompassing the cart module. So there is some issue because the system doesn't find what it's looking for.
In the checkout cart view, the code is actually normally this:
<div class="hikashop_cart_product_quantity_delete">
<a class="hikashop_no_print" href="<?php echo $delete_url; ?>" onclick="var qty_field = document.getElementById('<?php echo $this->last_quantity_field_id;?>'); if(qty_field){qty_field.value=0; return window.checkout.submitCart(<?php echo $this->step; ?>,<?php echo $this->module_position; ?>); } return false;" title="<?php echo JText::_('HIKA_DELETE'); ?>">
<i class="fa fa-times-circle"></i>
</a>
</div>
You can see that the delete button in the checkout calls the window.checkout.submitCart function after setting the quantity input field in the checkout to 0. That's what you should do in your view override of the show_block_cart.