There is no device called "lo". That is a device type, not a device. Loopback devices are lo0, lo1, etc. There is a device group "lo" however. Best practice is to use the lo0 device unless you have multiple loopback devices.
You did not include a dmesg, but if you had, you may not see the "em" devices you are attempting to configure.....as mentioned already.
I have never used any "builder" application, and cannot answer any questions about your input to one, out the output produced.
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