How to add Adserver to test?

Hello,

I have a problem that i cant resolve for almost a week,

I have published my channel and want to simply see if ads will appear on my videos.

In JSON feed I have specified that Ad should show at 00:00:07 second of the videos.

But I have problem with monetization(already enrolled) part with AdServer, the server that Roku provides doesn't work.

Is there any free AdServer that is simple and I can just get link from it and place it in AdServerURL or do I need to write on my own whole .xml with ads?

I dont wan't to earn money yet, just want to see that the Ad will be shown on video, for testing purpose.

Do I need to provide the Ads for AdServer on my own or how does it work?

I want an easy solution it could even be only one Ad, can someone provide a link to server and to app-ads.txt?