The installer just says that it fails, and nothing more. I don’t know how to debug this.
I also tried removing the existing installation, but that didn’t help.
Update
There is an error log under Window > Installer Log:
Nov 4 18:23:13 kn-macbook-air Installer[12808]: Failed to load specified background image
Nov 4 18:23:28 kn-macbook-air installd[2868]: PackageKit: ----- Begin install -----
Nov 4 18:23:29 kn-macbook-air installd[2868]: PackageKit: Install Failed: Error Domain=PKInstallErrorDomain Code=110 "An error occurred while extracting files from the package “6440_Scaler-2.7.0.pkg”." UserInfo={NSLocalizedDescription=An error occurred while extracting files from the package “6440_Scaler-2.7.0.pkg”., NSURL=file:///Users/alinz/Downloads/6440_Scaler-2.7.0.pkg#Scaler2.pkg, PKInstallPackageIdentifier=com.tonicbits.pkg.Scaler2, NSUnderlyingError=0x116175be0 {Error Domain=PKXARArchiveErrorDomain Code=101 "archive open failed" UserInfo={NSURL=file:///Users/alinz/Downloads/6440_Scaler-2.7.0.pkg, NSFileOwnerAccountID=501, NSFileHFSTypeCode=0, NSFileSystemFileNumber=18611785, NSFileExtensionHidden=false, NSFileSystemNumber=16777229, NSFileSize=1452750322, NSFileGroupOwnerAccountID=20, NSFileHFSCreatorCode=0, NSFileOwnerAccountName=alinz, NSFilePosixPermissions=420, NSFileCreationDate=2022-11-04 15:21:49 +0000, NSFileType=NSFileTypeRegular, NSFileProtectionKey=NSFileProtectionCompleteUntilFirstUserAuthentication, NSFileGroupOwnerAccountName=staff, NSFileReferenceCount=1, NSFileModificationDate=2022-11-04 15:22:42 +0000, NSLocalizedDescription=archive open failed}}} {
NSLocalizedDescription = "An error occurred while extracting files from the package \U201c6440_Scaler-2.7.0.pkg\U201d.";
NSURL = "file:///Users/alinz/Downloads/6440_Scaler-2.7.0.pkg#Scaler2.pkg";
NSUnderlyingError = "Error Domain=PKXARArchiveErrorDomain Code=101 \"archive open failed\" UserInfo={NSURL=file:///Users/alinz/Downloads/6440_Scaler-2.7.0.pkg, NSFileOwnerAccountID=501, NSFileHFSTypeCode=0, NSFileSystemFileNumber=18611785, NSFileExtensionHidden=false, NSFileSystemNumber=16777229, NSFileSize=1452750322, NSFileGroupOwnerAccountID=20, NSFileHFSCreatorCode=0, NSFileOwnerAccountName=alinz, NSFilePosixPermissions=420, NSFileCreationDate=2022-11-04 15:21:49 +0000, NSFileType=NSFileTypeRegular, NSFileProtectionKey=NSFileProtectionCompleteUntilFirstUserAuthentication, NSFileGroupOwnerAccountName=staff, NSFileRefere
Nov 4 18:23:29 kn-macbook-air Installer[12808]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
Nov 4 18:23:29 kn-macbook-air Installer[12808]: Displaying 'Install Failed' UI.
Nov 4 18:23:29 kn-macbook-air Installer[12808]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'.