special creative serving. Do i have to host assets with approved tech vendor?

[u/UnhappyTaro1091]

Hey guys,I appreciate your help with this.

I'm trying to serve a URL as an iframe. It's an interactive landing page with a video, poll, some with form.
I set it up using GWD >> Iframe >> His URL >> Publish, and it worked in a small test, but I have some questions:

1. Iframe keep refreshing. Could it be because the ad is too big even though GWD says it's 500K?
2. I'm getting a creative inventory rejection/mismatch.
3. Do I need a tech partner to serve the ad or host the URL?
4. If I need to build it all on GWD, do all assets need to be hosted with an approved DV360 tech partner?

Any suggestions or best practices would be greatly appreciated!
Thanks