Time machine will not backup message says network problem

I am using time machine for my imac. Stays in preparing mode then stops with message of Network Problem.

What is the macOS version installed in iMac?

High Sierra 10.13.6

You should do the power cycle of My Cloud Home device and also reboot your iMac. Then try to create a Time Machine backup. If issue still persists, follow the steps described in below mentioned link: