Problem using Stream in Tokio Task

With following code, I get error that "implementation of std::ops::FnOnce is not general enough" and "no two async blocks, even if identical, have the same type. consider pinning your async block and casting it to a trait object". The error is on spawn line, and detail line number points to the whole closure of inner_stream call in then. I tried to pin the closure or the block, nothing seems to work. Maybe I did not do it right. How can I fix this? async fn inner_stream(a: TypeA, b: TypeB, c: T...