cannot use func literal (type func(interface {})) as type func(interface {}) error in argument to reactor.OnNext

[gcxfd]

❯ ls

go.mod  go.sum  ping-pong.pb.go  ping-pong_test.go

❯ go test

go build github.com/rsocket/rsocket-rpc-go/examples/ping-pong: no non-test Go files in /Users/z/go/pkg/mod/github.com/rsocket/[email protected]/examples/ping-pong
# github.com/rsocket/rsocket-go/rx
/Users/z/go/pkg/mod/github.com/rsocket/[email protected]/rx/subscriber.go:12:60: cannot use func literal (type func(interface {})) as type func(interface {}) error in argument to reactor.OnNext
FAIL    rmw [build failed]

❯ go version
go version go1.15 darwin/amd64
❯ cat go.mod

module rmw

go 1.15

require (
        github.com/golang/protobuf v1.4.2
        github.com/jjeffcaii/reactor-go v0.2.2
        github.com/rsocket/rsocket-go v0.5.13
        github.com/rsocket/rsocket-rpc-go v0.0.1
        github.com/stretchr/testify v1.6.1
)