Google Tag Manager Debugging iOS

Question

I'm new to Google Tag Manager, so my question might be funny. I have included the GTM SDK in the iOS app. In the console, I see

GoogleTagManager verbose: GoogleAnalytics 3.14 -[GAIBatchingDispatcher  persist:] 
(GAIBatchingDispatcher.m:517): Saved hit

I am using the code snippet below to send a trigger.

[dataLayer push:@{
                  @"event": @"openScreen",
                  @"screenName": screenName
                  }];

I could not see any user in Google Analytics, I do not know how to debug GTM. I tried to use Charles to track mobile phone traffic, and I saw that the request was sent to GTM and GA.

I don’t know how to debug GTM and find where the problem is? Is there any debugging method for GTM?