This is the response I get
{"message":"A Content-Type header must be supplied with a request payload.","error":"no-content-type","httpCode":415,"httpReason":"Unsupported Media Type"}
and the trace
#0 /var/www/html/w/extensions/VisualEditor/includes/ApiParsoidTrait.php(279): ApiVisualEditorEdit->requestRestbase(Object(Title), 'POST', 'transform/html/...', Array, Array)
#1 /var/www/html/w/extensions/VisualEditor/includes/ApiParsoidTrait.php(296): ApiVisualEditorEdit->postData('transform/html/...', Object(Title), Array, Array, NULL)
#2 /var/www/html/w/extensions/VisualEditor/includes/ApiVisualEditorEdit.php(189): ApiVisualEditorEdit->postHTML(Object(Title), '<!doctype html>...', Array, NULL)
#3 /var/www/html/w/extensions/VisualEditor/includes/ApiVisualEditorEdit.php(163): ApiVisualEditorEdit->getWikitextNoCache(Object(Title), Array, Array)
#4 /var/www/html/w/extensions/VisualEditor/includes/ApiVisualEditorEdit.php(349): ApiVisualEditorEdit->getWikitext(Object(Title), Array, Array)
#5 /var/www/html/w/includes/api/ApiMain.php(1593): ApiVisualEditorEdit->execute()
#6 /var/www/html/w/includes/api/ApiMain.php(529): ApiMain->executeAction()
#7 /var/www/html/w/includes/api/ApiMain.php(500): ApiMain->executeActionWithErrorHandling()
#8 /var/www/html/w/api.php(90): ApiMain->execute()
#9 /var/www/html/w/api.php(45): wfApiMain()
#10 {main}