In your developer.roku.com account --> Manage My Channels --> Monitization, under ad server url, you should have something that looks like this:
Also in your Wordpress, are you using this plugin - it might be helpful:
You create it in Google Ads Manager depending on your settings.
I have setup my Adbreaks through my WP Smart TV and I see the adbreaks in the Json feed but no ads plays on any of my videos. I also use Google Ads to set it up. On top of that I cannot even change anything from my Develop dashboard because I get error not allowing me to see my channel info. I contact Roku just waiting on answer.
What’s your network- were you able to get the ass server working on a channel with less than 5000 subscribers?