Hi Arno, I agree with Magda that your store, while selling products from multiple niches, looks like it has a strong consistent branding and appeals to one type of customer - perfect. You mentioned that you have plenty of traffic and yet your sales are still low. I would suggest improving your FB ads even further, test different images, CTAs, text, with emojis or without and so on.
FB ads rarely work at a first try [as most things in business], so tweak them until you find the best strategy that works for you. You need to get the traffic that is more relevant to your niche, and from people who are already actively looking to buy. You attract more relevant traffic by using the right keywords - not all keywords are equal, there are four types of keyword intent. They are:
Navigational, where users search for a particular website.
Informational, where users search for the answer to a question.
Investigational, where users search for information that may eventually lead to transaction.
Transactional, where users are ready to buy.
In order to drive more traffic that converts, you need to be using the transactional keywords in your ads copy, website copy and so on.
Give me a shout if you'd like to learn more!