Recent time some of the peoples are suffering with .aab build failed error( i believe this thread will be helpful to somewhat)…
Though plenty of suggestions are there for apk build failed error, there is no any guide for .aab build error(I think - Suppose if it exists, add it in the reply) . So i am making for this mini guide and also enabling this guide into wiki mode there by even in future if any other errors found users can add the error along with solution…
Since aab build is more sensitive (just like building apk in beta mode) it wont allow us to build even for single error in any of the screens, if found…
Possible reasons for build errors are,
1. Incompletion of blocks
It is quite common, accidentally we may fail to complete the block connection, (apk will complie 
) but .aab wont allow it.
Actual error log
.
Hint: Did you see the highlight part
?,
If you are able to find the difference You are well good 
But keep in mind, .aab will build if there is error found with YELLOW error count, it means Blocks are connected but extra non usable only existing
If are already know about all those error and solution, Just skip this guide
Please correct me if i am wrong…
Suggestions are welcome
