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I tested the process below on Mac OS Mojave and it still works.

Original post was created by Bryan at wrmem.net 

Network engineers on Windows have been using the lightweight and open source TFTPD32, for years But for those of us who have evolved and moved to the Mac we have found a couple short comings due to the increased security and sandboxing requirements set by apple. Luckily there’s a built in tftp daemon that you can use in a pinch if you know a couple little tricks.
Here is a link to another post for apple OS Sierra Sky579x.bligspot.com

By default tftpd uses the following folder:
which is hidden in finder, but can be accessed by using “go to folder” or hitting Command+Shift+G and entering /private/tftpboot

To launch the daemon run the following commands:
sudo launchctl load -F /System/Library/LaunchDaemons/tftp.plist
sudo launchctl start com.apple.tftpd
Be sure Read/Write/eXecute permissions are set on the tftpboot folder and any files you wish to transfer:
sudo chmod 777 /private/tftpboot
sudo chmod 777 /private/tftpboot/*
If you’ll be transferring a file TO your TFTP server, the file will technically need to exist on the server beforehand so create it with touch. For example:
sudo touch /private/tftpboot/running-config
sudo chmod 777 /private/tftpboot/running-config
To unload and shutdown your tftp daemon you can run the following command.
sudo launchctl unload -F /System/Library/LaunchDaemons/tftp.plist
If you’d like a graphical front end for launching tftp then check out the great TftpServer. I have found this application not as reliable so I have fallen back to using the built in TFTP server. 
Now you can start transferring your files.

Happy TFTP'ng