I'm not sure I fully understand the issue or what you're trying to do here. Maybe @hyangah knows?

The error message is not very comprehensive (I suspect the gomobile/gobind didn't stop early when it observed unsupported types so the go command instead produced this error later while compiling incompletely generated glue code).
https://pkg.go.dev/golang.org/x/mobile/cmd/gobind#hdr-Type_restrictions has the set of types gobind (gomobile bind) supports. I guess use of slice in ChatStateHandler can be problematic, and, even though I don't know what's entity.Token but that can be also an issue. You can verify to see what's generated by running the gobind command directly. (golang.org/x/mobile/bind).

I figured out that interfaces that are injected into constructors exposed to Android cannot have methods receiving or returning types that are not defined inside the same package that gomobile compiles.

entity.Token is a simple struct defined in another package

type Token struct {
        AccessToken  string
        RefreshToken string
}

func NewToken(accessToken, refreshToken string) *Token {
        return &Token{
                AccessToken:  accessToken,
                RefreshToken: refreshToken,
        }
}

I can solve the problem by defining a Token inside the mobile package and the map the entity.Token internally to mobile.Token

It would be nice to have the ability to use models from external packages as arguments and return values in methods of interfaces. So that I can return the model directly from the internal/entity package instead of redefining every model in the mobile package.

├── internal
│   ├── constants.go
│   ├── entity
│   │   └── models.go
│   ├── interfaces
│   │   ├── auth.go
│   │   ├── chat.go
│   │   └── utils.go
│   └── repository
│       ├── grpc
│       │   ├── authrepo
│       │   └── chatrepo
│       └── http
│           ├── authrepo
│           └── chatrepo
├── mobile
│   ├── auth.go
│   ├── authstatehandler.go
│   ├── chat.go
│   ├── chatstatehandler.go
│   └── messagereceiver.go