Some reasons that A2Reviews cannot add snippet code to your Shopify theme, you can do it manually.
* Display total reviews widget on the product page:
In your theme, open this file sections/product-template.liquid. Add snippet code below to anywhere want to display total reviews.
{% include 'a2reviews-total' %} or with ajax load
{% render 'a2reviews-total' product:product %}
* Display total reviews widget on the collection page:
Each Shopify theme can have different file names to display the product list on the collection page. Find a suitable position to display total reviews. Snippet code below you can add.
{% include 'a2reviews-total' type:'collection' %} (new version){% include 'a2reviews-collection-total' %} (Removed)and user render with ajax load
{% render 'a2reviews-total' type:'collection' product:product %} (new version){% render 'a2reviews-collection-total' product:product %} (Removed)
* Main reviews / QA widget snippet code, (Mostly added in the file templates/product.liquid)
{% include 'a2reviews-widget' %}or in ajax load
{% render 'a2reviews-widget' product:product %}
QA Widget Snippet Code
{% include 'a2reviews-widget' type:'QA' %} (new version){% include 'a2reviews-qa-widget' %} (Removed)or
{% render 'a2reviews-widget' type:'QA' product:product  %} (new version){% render 'a2reviews-qa-widget' product:product %} (Removed)