<div class="products-list-page main-content" fix-sidebar set-width>
  <div class="content">

    <products-list ng-repeat="category in listCtrl.categories" category="category">
      <product-box class="product-box" ng-repeat="product in category.products" product="product">
        <a ui-sref="base.admin.products.edit({id: product.id})">Edit</a>
      </product-box>

      <div class="add-product-box">
        <div class="product-box-shadow">
          <a ui-sref="base.admin.products.create">
            <div class="fa-stack">
              <i class="fa fa-fw fa-stack-2x fa-circle-thin"></i>
              <i class="fa fa-fw fa-stack-1x fa-plus"></i>
            </div>
            <div class="title">Add new product</div>
          </a>
        </div>
      </div>
    </products-list>
  </div>
</div>

<div class="products-list-page main-content" fix-sidebar set-width>
  <div class="content">

    <products-list ng-repeat="category in listCtrl.categories" category="category">
      <product-box class="product-box" ng-repeat="product in category.products" product="product">
        <a ui-sref="base.admin.products.edit({id: product.id})">Edit</a>
      </product-box>

      <div class="add-product-box">
        <div class="product-box-shadow">
          <a ui-sref="base.admin.products.create({product_category_id: category.id})">
            <div class="fa-stack">
              <i class="fa fa-fw fa-stack-2x fa-circle-thin"></i>
              <i class="fa fa-fw fa-stack-1x fa-plus"></i>
            </div>
            <div class="title">Add new product</div>
          </a>
        </div>
      </div>
    </products-list>
  </div>
</div>

Add missing product_category_id to the create product url
Add missing product_category_id to the create product url
