childpages cant access by short url (relative url)

Hello,
I recently moved my wordpress site from 1 host to another.
I have copied all files and the full database. The domain-name has not changed.
Their is only one problem,
I ‘m using href links like /postname/ instead of https://www.domainname.com/parent/postname/
but it does not want to redirect:
/postname/ goes to https://www.domainname.com/postname/ and gives a 404 page

all other links are working fine
/ goes to https://www.domainname.com/
/parent/ goes to https://www.domainname.com/parent/
/postname/ goes to https://www.domainname.com/postname/ and gives a 404 page
this used to be working on my old host