401 on image preview url

So Im trying to get an image preview out of a bucket. im using a nextjs api to provide file data to my frontend, including a preview url. from other posts I gathered that i need to "construct" the url myself which i did and that worked ("endpoint/storage/buckets/[id]/files/[id]/preview?project=[id]"). my issue now is that the image tag in my component cant get the preview because it returns with 401. im kinda idea-less on how to work around this / fix this in a proper way.