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with sign in to Microsoft account and store windows phone 8.1
As posted already several hundred times in this community, the Store for WP8.1 devices closed for good on December 16th 2019. That's it, it's gone and it's not coming back.
The signing in problem used to happen every few months and so far MS managed to fix it within a few days or a week. Given that all support for WP8.1 ended back in July 2017 and with the app Store closed since last month they may decide it makes no sense to fix it this time, I don't know. You can only wait and see, however there is no real point in still using a WP8.1 device any more.
If your phone is supported for Windows 10 Mobile, you can upgrade it following the procedure I have given further above on this page.
I don't know why so many people seek assistance and help without providing basic information like which device they are using and which OS version is it running on, it would make it much easier for others to provide useful suggestions without wasting anyone's time.