cannot create bootable usb for big sur, error in terminal

hello,

I have beta 4 downloaded in applications folder.

i formatted usb , type command in terminal and getting this error below. how can i fix this to make bootable usb installer?

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objc[775]: Class IASNightInstallSupport is implemented in both /System/Library/PrivateFrameworks/IASUtilities.framework/Versions/A/IASUtilities (0x7fff8bf21d78) and /Applications/Install macOS Big Sur Beta.app/Contents/Frameworks/OSInstallerSetup.framework/Versions/A/Frameworks/IAESD.framework/Versions/A/Frameworks/IAInstallerUtilities.framework/Versions/A/IAInstallerUtilities (0x101bb0ac0). One of the two will be used. Which one is undefined.

objc[775]: Class IASSystemInformation is implemented in both /System/Library/PrivateFrameworks/IASUtilities.framework/Versions/A/IASUtilities (0x7fff8bf21eb8) and /Applications/Install macOS Big Sur Beta.app/Contents/Frameworks/OSInstallerSetup.framework/Versions/A/Frameworks/IAESD.framework/Versions/A/Frameworks/IAInstallerUtilities.framework/Versions/A/IAInstallerUtilities (0x101bb0bd8). One of the two will be used. Which one is undefined.

Couldn't mount dmg /Applications/Install macOS Big Sur Beta.app/Contents/SharedSupport/SharedSupport.dmg (error code 110)/Applications/Install macOS Big Sur Beta.app does not appear to be a valid OS installer application.