Fix this issue in to_vec method.

.changelog/unreleased/bug-fixes/1004-fix-packet-sequence-encoding.md

@@ -0,0 +1,2 @@
+- Encode packet sequence into a big endian bytes.
+  ([\#1004](https://github.com/cosmos/ibc-rs/pull/1004))

ibc-core/ics04-channel/src/handler/timeout.rs

@@ -229,14 +229,13 @@ where
             }
             let seq_recv_path_on_b =
                 SeqRecvPath::new(&msg.packet.port_id_on_b, &msg.packet.chan_id_on_b);
-            let value = u64::from(msg.packet.seq_on_a).to_be_bytes().to_vec();
 
             client_state_of_b_on_a.verify_membership(
                 conn_end_on_a.counterparty().prefix(),
                 &msg.proof_unreceived_on_b,
                 consensus_state_of_b_on_a.root(),
                 Path::SeqRecv(seq_recv_path_on_b),
-                value,
+                msg.packet.seq_on_a.to_vec(),
             )
         } else {
             let receipt_path_on_b = ReceiptPath::new(

ibc-core/ics24-host/types/src/identifiers/sequence.rs

@@ -1,5 +1,4 @@
 use ibc_primitives::prelude::*;
-use ibc_primitives::ToVec;
 
 use crate::error::IdentifierError;
 
@@ -50,10 +49,9 @@ impl Sequence {
         Sequence(self.0 + 1)
     }
 
-    /// Encodes the sequence number into a `Vec<u8>` using
-    /// `prost::Message::encode_to_vec`.
+    /// Encodes the sequence number into a byte array in big endian.
     pub fn to_vec(&self) -> Vec<u8> {
-        self.0.to_vec()
+        self.0.to_be_bytes().to_vec()
     }
 }