It is rather unfortunate, but twrp.img could not be transferred to the Xiaomi phone simply because the computer from which it was done, did not have a USB 2.0 port.
To overcome this, connect a USB 2.0 hub to the USB 3.0 port of the laptop. Then connect the Xiaomi phone USB cable to the USB 2.0 port on the hub.
After doing above, using fastboot, twrp.img transfers without any problem.
Those of us who do not have older laptops can use the above method to flash twrp.img to the phone.