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Hi, This is Aamit Sainii, If your domain authority is not increasing even after creating high quality backlinks, I think there is no fault of Moz. It depends on Google most of the time until the crawler of Google will not notice that backlinks which directed to your website, till then Moz or any other DA checker will not count them. In my view you have to wait till google crawler notices them or you create backlinks again.

@solenneginx Hi, This Aamit Saini It is good point to purchase expired domain instead of new one. Expired domain already have some backlinks, on this point it is a good move, but if you purchased new one that will be better, because you can select it as per your niche which will suit your blog and in the last it will be as per your choice.