Confluence Server 7.16 Rest API update content

Hello,

I’m using confluence server 7.16.4 and I’m trying to update the page content via rest api. Even I use the documentation provided at https://docs.atlassian.com/ConfluenceServer/rest/7.16.4/
I always get a status 400, Bad Request.
Any idea how I can get closer of what is going wrong?
Thanks in advance

Ralph