It seems like it fixed my problems with help from the Onlyoffice forum! But I will update here too so that others can maybe get some ideaâs from this.
Onlyoffice:
default.json -> ârejectUnauthorizedâ to false.
local.json -> âheaderâ: âAuthorizationJwtâ from âheaderâ: âAuthorizationâ
supervisorctl restart all
Nexcloud:
config/config.php ->
âonlyofficeâ => array (
âverify_peer_offâ => true,
âjwt_headerâ => âAuthorizationJwtâ
)