Svelte routing on production not work with dynamic build links (Svelte Router SPA)

fetching a json-file with a "url"-string. With this I'm building an url in svelte. For the routing I'm using Svelte Router SPA. In Dev-Mode everything is working fine but after deploying the pages are not found. This happens only on "dynamic-build-links" through the json-feed. If I write it manually it works.

thanks for helping.

routes.js

{
      name: 'prod/:product',
      component: PublicProduct,
      }

package.json

"start": "sirv public -s"

Svelte Router SPA