Mopub very low fillrate

After banned from admob i try mopub but my fill rate is very low…i have 100.000 request 21000 impressions,what can i do?

switch the network

Are you using only Mopub? If so the fill rate will be low. You should add at least 1 network. Note that you can add html banner tags (This means that you don’t have to update the app) AFAIK, not many networks support html tags (Leadbolt, Smaato, and Lifestreet do). There are also some networks that have a server-to-server arrangement with Mopub. I backfill with Appbrain banners (The banner opens the intersatial)

how can I use back fill please help