diff --git a/openapi-def.yaml b/openapi-def.yaml
index d9cb668..7ecbfbf 100644
--- a/openapi-def.yaml
+++ b/openapi-def.yaml
@@ -425,6 +425,29 @@ paths:
           $ref: '#/components/responses/Unauthorized'
         default:
           $ref: '#/components/responses/Default'
+  /api/users/interop:
+    get:
+      operationId: users-list-all-interop
+      summary: List all remote users
+      tags:
+        - Users
+      security:
+        - bearer: []
+      responses:
+        200:
+          description: Ok
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: string
+        400:
+          $ref: '#/components/responses/BadRequest'
+        401:
+          $ref: '#/components/responses/Unauthorized'
+        default:
+          $ref: '#/components/responses/Default'
   /api/chats:
     get:
       operationId: list-chats
diff --git a/src/api/interop.rs b/src/api/interop.rs
index 5262bc7..1c3c069 100644
--- a/src/api/interop.rs
+++ b/src/api/interop.rs
@@ -98,13 +98,13 @@ async fn interop_pay(
     Ok(StatusCode::OK)
 }
 
-#[derive(Serialize)]
-struct ListUsers {
-    users: Vec<String>,
-    expires_in: u32,
+#[derive(Deserialize, Serialize)]
+pub struct InteropListUsers {
+    pub users: Vec<String>,
+    pub expires_in: u32,
 }
 
-async fn list_users(EState(state): State, _: InteropAuth) -> Result<Json<ListUsers>, Error> {
+async fn list_users(EState(state): State, _: InteropAuth) -> Result<Json<InteropListUsers>, Error> {
     let conn = state.conn().await?;
     let stmt = conn.prepare_cached(
         "select case when a.name = 'personal' then u.name else concat(u.name, ':', a.name) end as account from accounts a join users u ON a.\"user\" = u.id;",
@@ -115,7 +115,7 @@ async fn list_users(EState(state): State, _: InteropAuth) -> Result<Json<ListUse
         .into_iter()
         .map(|row| row.get(0))
         .collect();
-    Ok(Json(ListUsers {
+    Ok(Json(InteropListUsers {
         users: accounts,
         expires_in: 42,
     }))
diff --git a/src/api/mod.rs b/src/api/mod.rs
index c69dbf0..59ed851 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -11,6 +11,8 @@ use axum::{
 use bank_core::{ApiError, make_schemas, pagination::RequestPagination};
 use jsonwebtoken::{DecodingKey, EncodingKey};
 use serde::{Deserialize, Serialize, de::DeserializeOwned};
+use tokio::{sync::Mutex, time::Instant};
+use tracing::error;
 use tracing_error::SpanTrace;
 
 pub use axum::extract::State as EState;
@@ -28,6 +30,7 @@ mod transactions;
 mod user;
 
 pub use interop::router as interop_router;
+use transactions::TARGET_NOT_FOUND;
 
 use crate::config::Meta;
 
@@ -104,6 +107,7 @@ pub enum InnerError {
 }
 
 impl Error {
+    #[track_caller]
     pub fn new(inner: InnerError) -> Self {
         let trace = if cfg!(debug_assertions) || inner.internal() {
             Some(SpanTrace::capture())
@@ -121,34 +125,56 @@ impl Error {
 }
 
 impl<T: Into<InnerError>> From<T> for Error {
+    #[track_caller]
     fn from(value: T) -> Self {
         Error::new(value.into())
     }
 }
 
 impl From<deadpool_postgres::PoolError> for InnerError {
+    #[track_caller]
     fn from(value: deadpool_postgres::PoolError) -> Self {
         Self::Pool(value)
     }
 }
 impl From<tokio_postgres::Error> for InnerError {
+    #[track_caller]
     fn from(value: tokio_postgres::Error) -> Self {
         Self::Postgres(value)
     }
 }
 
 impl From<password_auth::ParseError> for InnerError {
+    #[track_caller]
     fn from(value: password_auth::ParseError) -> Self {
         Self::PHCParse(value)
     }
 }
 
 impl From<ApiError<'static>> for InnerError {
+    #[track_caller]
     fn from(value: ApiError<'static>) -> Self {
         InnerError::Plain(value)
     }
 }
 
+impl From<InteropError> for InnerError {
+    #[track_caller]
+    fn from(value: InteropError) -> Self {
+        match value {
+            InteropError::TransactionTargetNotFound => TARGET_NOT_FOUND.into(),
+            InteropError::Http(err) => {
+                error!("{err}");
+                ApiError::INTERNAL_SERVER_ERROR.into()
+            }
+            InteropError::Other(response) => {
+                error!("{response:?}");
+                ApiError::INTERNAL_SERVER_ERROR.into()
+            }
+        }
+    }
+}
+
 impl InnerError {
     pub const fn internal(&self) -> bool {
         match self {
@@ -280,8 +306,20 @@ pub struct InteropState {
     pub secret: String,
     pub client: reqwest::Client,
     pub url: url::Url,
+    pub user_url: url::Url,
     pub pay_url: url::Url,
-    pub prefix: String,
+    pub suffix: String,
+    pub users: Mutex<Option<(InteropUsers, Instant)>>,
+}
+
+pub enum InteropError {
+    TransactionTargetNotFound,
+    Http(reqwest::Error),
+    Other(reqwest::Response),
+}
+
+pub struct InteropUsers {
+    names: Vec<String>,
 }
 
 impl AppState {
diff --git a/src/api/transactions.rs b/src/api/transactions.rs
index bdde3bc..90942f5 100644
--- a/src/api/transactions.rs
+++ b/src/api/transactions.rs
@@ -13,7 +13,7 @@ use uuid::Uuid;
 use crate::model::{Accounts, Transactions, Users};
 
 use super::{
-    AppState, EState, Error, InteropState, Json, State,
+    AppState, EState, Error, InteropError, InteropState, Json, State,
     auth::Auth,
     socket::{SocketEvent, SocketMessage},
 };
@@ -296,7 +296,7 @@ impl MakePayment {
     }
 }
 
-const TARGET_NOT_FOUND: ApiError<'static> = ApiError::const_new(
+pub const TARGET_NOT_FOUND: ApiError<'static> = ApiError::const_new(
     StatusCode::NOT_FOUND,
     "transaction.target.not_found",
     "Not Found",
@@ -334,21 +334,7 @@ pub async fn make_payment(
             if amount % 100 != 0 {
                 todo!()
             }
-            if let Err(err) =
-                send_interop_payment(&interop, &from.name, &user, (amount / 100) as u32).await
-            {
-                return Err(match err {
-                    InteropError::NotFound => TARGET_NOT_FOUND.into(),
-                    InteropError::Http(err) => {
-                        error!("{err}");
-                        ApiError::INTERNAL_SERVER_ERROR.into()
-                    }
-                    InteropError::Other(response) => {
-                        error!("{response:?}");
-                        ApiError::INTERNAL_SERVER_ERROR.into()
-                    }
-                });
-            }
+            send_interop_payment(&interop, &from.name, &user, (amount / 100) as u32).await?;
             transaction
         }
         AccountTarget::Selector(selector) => {
@@ -498,12 +484,6 @@ impl<'a, T: GenericClient> TransactionBuilder<'a, T> {
     }
 }
 
-enum InteropError {
-    NotFound,
-    Http(reqwest::Error),
-    Other(reqwest::Response),
-}
-
 async fn send_interop_payment(
     interop: &InteropState,
     from: &str,
@@ -513,6 +493,7 @@ async fn send_interop_payment(
     let response = interop
         .client
         .post(interop.pay_url.clone())
+        .bearer_auth(&interop.secret)
         .json(&serde_json::json!({
             "from": from,
             "to": to,
@@ -525,7 +506,7 @@ async fn send_interop_payment(
         return Ok(());
     }
     if response.status() == StatusCode::NOT_FOUND {
-        return Err(InteropError::NotFound);
+        return Err(InteropError::TransactionTargetNotFound);
     }
     Err(InteropError::Other(response))
 }
diff --git a/src/api/user.rs b/src/api/user.rs
index 0c1894d..ca9a4cf 100644
--- a/src/api/user.rs
+++ b/src/api/user.rs
@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::{sync::Arc, time::Duration};
 
 use axum::{
     Router,
@@ -11,18 +11,24 @@ use bank_core::{
     transaction::{FullTransaction, TransactionQuery},
     user::{User, UserAccounts, UserBalance},
 };
+use concread::cowcell::asynch::CowCell;
+use futures_util::lock::Mutex;
 use garde::Validate;
+use reqwest::StatusCode;
 use serde::{Deserialize, Serialize};
-use tracing::instrument;
+use serde_json::json;
+use tokio::time::Instant;
+use tracing::{error, instrument};
+use url::Url;
 use uuid::Uuid;
 
 use crate::{
-    api::ApiError,
+    api::{ApiError, InteropUsers, interop::InteropListUsers},
     model::{Accounts, Transactions, Users},
 };
 
 use super::{
-    AppState, EState, Error, Json, PaginationQuery, Query, State,
+    AppState, EState, Error, InteropError, InteropState, Json, PaginationQuery, Query, State,
     auth::{Auth, Claims},
 };
 
@@ -36,6 +42,7 @@ pub(super) fn router() -> Router<Arc<AppState>> {
         .route("/@me/transactions", get(me_transaction_history))
         .route("/@me/password", put(change_password))
         .route("/", get(list_users))
+        .route("/interop", get(list_interop_users))
 }
 
 #[derive(Deserialize, Serialize)]
@@ -90,6 +97,66 @@ pub async fn list_users(
     Ok(Json(users))
 }
 
+async fn fetch_users(state: &InteropState) -> Result<Vec<String>, InteropError> {
+    let response = state
+        .client
+        .get(state.user_url.clone())
+        .bearer_auth(&state.secret)
+        .send()
+        .await
+        .map_err(InteropError::Http)?;
+    if response.status() != StatusCode::OK {
+        return Err(InteropError::Other(response));
+    }
+    let mut data = response
+        .json::<InteropListUsers>()
+        .await
+        .map_err(InteropError::Http)?;
+    for name in data.users.iter_mut() {
+        name.push('@');
+        name.push_str(&state.suffix);
+    }
+    Ok(data.users)
+}
+
+#[instrument(skip(state))]
+pub async fn list_interop_users(
+    EState(state): State,
+    _: Auth,
+) -> Result<Json<serde_json::Value>, Error> {
+    let Some(interop) = &state.interop else {
+        return Ok(Json(serde_json::Value::Array(vec![])));
+    };
+    let mut guard = interop.users.lock().await;
+    let names = match &mut *guard {
+        Some((users, time)) => {
+            if Instant::now().duration_since(*time) > Duration::from_secs(100) {
+                match fetch_users(interop).await {
+                    Ok(names) => {
+                        users.names = names;
+                    }
+                    Err(err) => {
+                        let _ = Error::from(err);
+                    }
+                };
+            };
+            users.names.as_slice()
+        }
+        None => {
+            match fetch_users(interop).await {
+                Ok(names) => {
+                    *guard = Some((InteropUsers { names }, Instant::now()));
+                }
+                Err(err) => {
+                    let _ = Error::from(err);
+                }
+            };
+            guard.as_ref().unwrap().0.names.as_slice()
+        }
+    };
+    Ok(Json(json!(names)))
+}
+
 #[instrument(skip(state))]
 pub async fn me_transaction_history(
     EState(state): State,
diff --git a/src/main.rs b/src/main.rs
index 31b00f0..933d4b6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,7 +7,7 @@ use bankserver::{
     setup_db,
 };
 use jsonwebtoken::{DecodingKey, EncodingKey};
-use tokio::{net::TcpListener, signal};
+use tokio::{net::TcpListener, signal, sync::Mutex};
 use tracing::{info, level_filters::LevelFilter};
 use tracing_error::ErrorLayer;
 use tracing_subscriber::{EnvFilter, Registry, layer::SubscriberExt};
@@ -45,9 +45,11 @@ async fn main() {
             .timeout(Duration::from_secs(2))
             .build()
             .unwrap(),
+        user_url: config.url.join("/_internal/users").unwrap(),
         pay_url: config.url.join("/_internal/pay").unwrap(),
         url: config.url,
-        prefix: config.prefix,
+        suffix: config.prefix,
+        users: Mutex::new(None),
     });
 
     let router = Router::new()