https://wordpress.org/support/topic/...ot-well-formed

Şurada basitçe yanıtlamışlar sorunu.

"If you are posting to a wordpress.com website, WordPress recently changed over all its sites to https so when you try to post to the http URL it is returning a 301 and the xmlrpc client you are using can't follow it and probably doesn't have the code to deal with https.

If you are using WordPress IXL library and functions, then the cure is to make sure this is the problem (go to the URL and see if it turns into https) and change the URL you are sending to."

URL'in https'e dönüşüp dönüşmediğine bakın diyor, gönderdiğiniz URL'i buna göre değiştirin diyor.