You receive an error 1641 after deploying an MSI (etc.) package.
Error code 1641, ERROR_SUCCESS_REBOOT_INITIATED, indicates, "The installer has initiated a restart. This message is indicative of a success."
By default, PDQ Deploy includes this code in the Success Codes. See, Install Step Properties.
External Microsoft Documentation - MsiExec.exe and InstMsi.exe Error Messages (for Developers)
PDQ Deploy Documentation - Install Step Properties