Well I found a bit more. The plugin was requesting /wp-content/plugins/spreadshop/js/spreadshop_config.js which wasn’t there. So I made the file myself with contents:
var spread_shop_config = {
shopName: 'meatandsteak',
locale: 'nl_NL',
prefix: '//shop.spreadshirt.nl',
baseId: 'myShop'
};
But it’s not working, new error: Cannot read property ‘shopProps’ of null
What is the correct contents of the config file?