It has shut down... Here is what is on there website :
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Nextpost shut down!
When we started to develop Nextpost the reason was to help people to manage their Instagram accounts and we always recommended to our users to use the Nextpost responsibly. We never intended to build a product for spamming, harassment etc.
But unfortunately, many people started to obtain the Nextpost products in illegal ways (nulled scripts) to modify and start to use them in unintended ways. Even there are many users who have bought the Nextpost for spamming only. This is totally against our policy.
It’s really hard for us to fight with all these illegal uses of Nextpost products. So we decided to close our services. We disabled all of our products from Envato Marketplace to stop all new sales.
You’ll still be able to use your site of Nextpost. If you’ve got a support extension, there is no need to worry. We’ll be able to answer all of your support tickets at https://support.getnextpost.io until the last day of your support extension.
If you’ve not saved a copy of your purchases, you can get them from download.getnextpost.io or you can contact us until 20 October 2018 to send them to you.
It’s sad to say goodbye. Sorry about that...