You sell online through your webshop, via marketplaces. There is a good response to your products, logistics on the road, good reviews. But now you want to keep going! Through to multiple sales channels. Adding a new marketplace, that can't be that difficult, can it?
Soon you will find out that it is not as easy as previously thought. The marketplaces have different requirements with regard to content. You lose the overview, the stock has to be managed across the various channels and you may also have products in fulfillment, which makes things even more complex.
Then you start looking for tooling, but that doesn't make it any clearer. Often you need a webshop or you will have to adapt it to be able to sell on (multiple) marketplaces.