I had strange timeouts yesterday so I gave up not knowing if it was HTB infrastructure or perhaps a WAF doing its job. Today I realised that my manual approach using a tool did not work but when I dumped file from Burp Suite and let it work with that it seems to work. I can´t see why but I am obviously missing something in the request. Gonna go back later and learn from it, now I at least have found something to work with.