Hello,
I just visited the mentioned website and read the comments. In the comments also mentioned the same issues, which are in your Android Studio console. Seems the version of the template is outdated and most of the packages are out dated.
And also, there is a possibility that, the template has written in Dart 1.x and currently you are using Dart 2.x.4.
I can see there are very few bidding on this job and, if you don't mind, I can have a look at this template.
But cannot gurrent that, it can be fixed.
Let me know if you like.
Best Regards,
Nadun De Silva