The main reason for not displaying the cpm ad is the ad pricing is not active.
After creating the CPM ad and activate it, advertiser need to activate the CPM pricing.
For this please go to the “Manage Targeting” in the manage ads section.
Now select the “Pricing” tab and you can see the “Activate” button.
After the activation the CPM pricing is deducted from the advertiser account balance.
Advertiser can activate the CPM pricing only if the ad is active.