Can make it work

Hi – I just need a simple pop up with two other products when someone put a specific product in the basket. But on the category-page when I (have the plugin activated and) press add to basket (tilføj til kurv) it put the product to the basket but the site is just standing and spinning… No pop ups, just keep spinning.
On the single product page nothing happens.
We do not need any special price or special bundle – just a pop whit these product we like to sell along.

EG: if somenone add this product (https://kalundborg-skov-park-have.dk/produkt/stihl-legetoejsmotorsav/) to the basket, then there should be a popup whit this product: https://kalundborg-skov-park-have.dk/produkt/stihl-fodbold/
No mater if the product is added from this site: https://kalundborg-skov-park-have.dk/produkt-kategori/tilbehor/boern-legetoej/ or directly from the product: https://kalundborg-skov-park-have.dk/produkt/stihl-legetoejsmotorsav/