question

Hi,

Check out the knowledge base article explaining no fill errors for more information on this issue.

If you are testing in EU, then no ads will be shown at all (no test ads either) because the amazon SDK is broken for over a month now with not a single helpful info from amazon on fixing the issue. The previous SDKs (5.81 & 5.8.2 ) are not sending ads to EU users either due to GDPR compliance and because amazon didn't do anything to assist developers in sending EU consent to the SDK and they don't even offer non-personalised ads to at least have a current solution until they figure out their broken SDK.
Looks like Amazon mobile ads network is going to die soon since most of their ads are shown to EU countries and they don't look like in a hurry to fix anything at all. Very disappointing, it used to be a such a great network for ads and had huge potential to grow globally...

Maybe your ad requests are for 1024x50? I am getting the no fill error on those ad sizes and amazon has not responded to my report. https://forums.developer.amazon.com/questions/180135/no-fill-error-on-ads-sized-1024x50.html