Because json_serializable_mobx >=1.0.0 depends on json_serializable_mobx_typehelpers ^4.0.0 which doesn't match any versions, json_serializable_mobx >=1.0.0 is forbidden.
So, because encointer_wallet depends on json_serializable_mobx ^1.0.0, version solving failed.
You can try the following suggestion to make the pubspec resolve:
* Consider downgrading your constraint on json_serializable_mobx: flutter pub add dev:json_serializable_mobx:^0.10.3
See pub get output: