Hi there,
I had the exact same issue and read this thread in a search for a solution. Thanks to the suggestion of Karst, I’ve copied my production webshop to a staging URL and deactivated my LiteSpeed Cache plugin. After that, the initial sync (step 4) from my staging website to Zettle worked perfectly.
@kvdleijnijdam Did you manage to make this work on your production site already? Would it be an option to deactivate the caching plugin, syncing products and then turning it on again?
Many thanks.
Jur