[myTarget debug] Current device's Instance Id is D346D6CE-3414-4C22-BFC8-B4DD4983B1C8, use this value in method withTestDevices() on ad instance in order to enable Test Mode.
MTRGNativeAd *nativeAd = [[MTRGNativeAd nativeAdWithSlotId:12345] withTestDevices:@[@"D346D6CE-3414-4C22-BFC8-B4DD4983B1C8"]];
or
MTRGNativeAd *nativeAd = [MTRGNativeAd nativeAdWithSlotId:12345];
[nativeAd withTestDevices:@[@"D346D6CE-3414-4C22-BFC8-B4DD4983B1C8", @"D346D6CE-3414-4C22-BFC8-B4DD4983B1C8"]];