Shopify Theme Development | Creating a 're-order' link for previous orders | Unable to chain multiple ID:quantity query strings

I am using Shopify and creating a re-order button within the file named order.liquid.

while trying to create the re-order button I have had a moderate level of success.

The script I attach does indeed add the items to the cart that were previously ordered. However, I have tried without adding the quantity (just adds 1 of each). Without the [] after the &quantityHERE= (just adds two of each even if it was previously only one item bought).

Heres the code that creates my half-working URL:

{% assign line_items_string = '/cart/' %}
{% for line_item in order.line_items %}

    {% if forloop.first == true %}

        {% assign line_items_string = line_items_string | append: 'add?id[]=' %}
        {% assign line_items_string = line_items_string | append: line_item.variant_id %}
        {% assign line_items_string = line_items_string | append: '&quantity[]=' %}
        {% assign line_items_string = line_items_string | append: line_item.quantity %}

    {% else %}

        {% assign line_items_string = line_items_string | append: '&id[]=' %}
        {% assign line_items_string = line_items_string | append: line_item.variant_id %}
        {% assign line_items_string = line_items_string | append: '&quantity[]=' %}
        {% assign line_items_string = line_items_string | append: line_item.quantity %}

    {% endif %}

{% endfor %}

<a href="{{ line_items_string }}" class="reorder-link">Re-order</a>

I am unable to get it to add the correct amount of items per line item even though the URL appears correct:

/cart/add?id[]=16220586868785&quantity[]=3&id[]=16220587360305&quantity[]=6&id[]=16220587622449&quantity[]=4&id[]=16221376479281&quantity[]=11&id[]=16221376348209&quantity[]=2&id[]=16221063938097&quantity[]=1&id[]=16221393682481&quantity[]=2

The fact the string ends with quantity 2 and will then add 2 of each item suggests it only uses the last declaration of quantity when dealing with the link. Therefore there must be a separator that can be used to distinguish between line items.

What is the separator that would go between each line items addition to the query string please? What goes after?

add?id[]=16220586868785&quantity[]=3**HERE**

I have tried using a , but admittedly this looks out of place followed by an &.

Edit

To help describe further what I have tried.

I am able to use the format ID:quantity if I:

1. want to go straight to checkout, the format is ID:quantity,ID:quantity.. so on.

2. only wish to add one item of a certain quantity to cart using add?ID:Quantity.

I need to know how to chain multiple to only add to cart. I don’t know the separator (that is a comma when pushing straight to checkout).