Hi Burhan! I am Tin an independent advisor and I will gladly assist you with this issue. I can see how frustrating this can be but here are some steps to resolve the issue.
*Check Minecraft/Microsoft account status, since Minecraft Premium accounts are now linked to Microsoft accounts, go to https://account.microsoft.com and sign in.
Confirm that your account still has Minecraft, Java Edition purchased and active.
Visit https://www.minecraft.net/en-us/profile to check if your game profile (e.g., Minecraft username and skin) appears normally.
*Try logging in via Official Minecraft launcher, to confirm your credentials, download and open the official Minecraft Launcher from minecraft.net/download.
Log in with your Microsoft account. If this works, it confirms your account is still valid and the issue is with Feather Client.
*Update or reinstall Feather Client, since Feather Client updates regularly, uninstall Feather Client completely then go to https://featherclient.com and download the latest version. Reinstall it and try logging in again.
*Check for background login blocker. Make sure nothing on your system is interfering, disable antivirus or firewall temporarily and try again. Run Feather Client as Administrator. Try using a different network connection or hotspot in case it's a network issue.
* Clear Feather Client cache. There may be corrupted cache files, navigate to this folder: C:\Users<YourUsername>\AppData\Roaming\Feather.
Delete or move the contents of the folder to a backup folder. Then restart Feather Client.
*Check for Java or System issues, make sure you have the latest version of Java installed (especially if Feather uses its own Java or asks you to install it). Try running the client on a different user account on your PC.
*Try Lunar Client or other premium launchers. To confirm it’s Feather-specific, download Lunar Client or Badlion Client. Try logging in using the same Microsoft credentials.