How to serialize Blob from Rust?

When I have a Motoko function like:

public shared func f(x: Blob): async () {

and try to pass it Encode!(b) from Rust, where b: &[u8], it complains about a wrong type.

How to pass blob type to a Motoko method?

Rust code

let req_id = agent.update(&callback.canister, &callback.func)

and Motoko code

    public shared func checkRequest(hash: Blob): async () {

I also tried

    public shared func checkRequest(hash: [Nat8]): async () {

BTW, should I write &(*&actix_request_hash.as_slice(),) or &actix_request_hash.as_slice() suits?

A Blob is a vector of bytes essentially, so in Rust it would be Vec<u8>. I think the following code would work

let req_id = agent.update(&callback.canister, &callback.func)