diff --git a/examples/cloud.rs b/examples/cloud.rs
index df59545..0cc34ed 100644
--- a/examples/cloud.rs
+++ b/examples/cloud.rs
@@ -1,11 +1,11 @@
 use clap::Parser;
-use std::sync::Arc;
 
 use scroll_proving_sdk::{
     config::{CloudProverConfig, Config},
     prover::{
         proving_service::{
-            GetVkRequest, ProveRequest, ProveResponse, QueryTaskRequest, QueryTaskResponse,
+            GetVkRequest, GetVkResponse, ProveRequest, ProveResponse, QueryTaskRequest,
+            QueryTaskResponse,
         },
         ProverBuilder, ProvingService,
     },
@@ -21,7 +21,7 @@ struct Args {
 }
 
 struct CloudProver {
-    endpoint: String,
+    base_url: String,
     api_key: String,
 }
 
@@ -29,7 +29,7 @@ impl ProvingService for CloudProver {
     fn is_local(&self) -> bool {
         false
     }
-    fn get_vk(&self, req: GetVkRequest) -> String {
+    fn get_vk(&self, req: GetVkRequest) -> GetVkResponse {
         todo!()
     }
     fn prove(&self, req: ProveRequest) -> ProveResponse {
@@ -43,7 +43,7 @@ impl ProvingService for CloudProver {
 impl CloudProver {
     pub fn new(cfg: CloudProverConfig) -> Self {
         Self {
-            endpoint: cfg.endpoint,
+            base_url: cfg.base_url,
             api_key: cfg.api_key,
         }
     }
diff --git a/examples/local.rs b/examples/local.rs
index b913150..4f25b3b 100644
--- a/examples/local.rs
+++ b/examples/local.rs
@@ -1,11 +1,11 @@
 use clap::Parser;
-use std::sync::Arc;
 
 use scroll_proving_sdk::{
     config::{Config, LocalProverConfig},
     prover::{
         proving_service::{
-            GetVkRequest, ProveRequest, ProveResponse, QueryTaskRequest, QueryTaskResponse,
+            GetVkRequest, GetVkResponse, ProveRequest, ProveResponse, QueryTaskRequest,
+            QueryTaskResponse,
         },
         ProverBuilder, ProvingService,
     },
@@ -26,7 +26,7 @@ impl ProvingService for LocalProver {
     fn is_local(&self) -> bool {
         true
     }
-    fn get_vk(&self, req: GetVkRequest) -> String {
+    fn get_vk(&self, req: GetVkRequest) -> GetVkResponse {
         todo!()
     }
     fn prove(&self, req: ProveRequest) -> ProveResponse {
diff --git a/src/config.rs b/src/config.rs
index e25320e..29291d2 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -36,7 +36,7 @@ pub struct ProverConfig {
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct CloudProverConfig {
-    pub endpoint: String,
+    pub base_url: String,
     pub api_key: String,
 }
 
diff --git a/src/prover/builder.rs b/src/prover/builder.rs
index f4036e1..a10f51d 100644
--- a/src/prover/builder.rs
+++ b/src/prover/builder.rs
@@ -47,11 +47,14 @@ impl ProverBuilder {
             circuit_type: self.cfg.prover.circuit_type,
             circuit_version: self.cfg.prover.circuit_version.clone(),
         };
-        let vk = self
+        let get_vk_response = self
             .proving_service
             .as_ref()
             .unwrap()
             .get_vk(get_vk_request);
+        if let Some(error) = get_vk_response.error {
+            anyhow::bail!("failed to get vk: {}", error);
+        }
 
         let key_signers: Result<Vec<_>, _> = (0..self.cfg.prover.n_workers)
             .map(|i| {
@@ -66,7 +69,7 @@ impl ProverBuilder {
                 CoordinatorClient::new(
                     self.cfg.coordinator.clone(),
                     self.cfg.prover.circuit_type,
-                    vec![vk.clone()],
+                    vec![get_vk_response.vk.clone()],
                     self.cfg.prover.circuit_version.clone(),
                     format!("{}{}", self.cfg.prover_name_prefix, i),
                     key_signers[i].clone(),
diff --git a/src/prover/proving_service.rs b/src/prover/proving_service.rs
index eb04f8f..19f2e76 100644
--- a/src/prover/proving_service.rs
+++ b/src/prover/proving_service.rs
@@ -2,9 +2,9 @@ use super::CircuitType;
 
 pub trait ProvingService {
     fn is_local(&self) -> bool;
-    fn get_vk(&self, req: GetVkRequest) -> String; // TODO: Result<String, Error>
-    fn prove(&self, req: ProveRequest) -> ProveResponse; // TODO: Result<ProveResponse, Error>
-    fn query_task(&self, req: QueryTaskRequest) -> QueryTaskResponse; // TODO: Result<QueryTaskResponse, Error>
+    fn get_vk(&self, req: GetVkRequest) -> GetVkResponse;
+    fn prove(&self, req: ProveRequest) -> ProveResponse;
+    fn query_task(&self, req: QueryTaskRequest) -> QueryTaskResponse;
 }
 
 pub struct GetVkRequest {
@@ -12,6 +12,11 @@ pub struct GetVkRequest {
     pub circuit_version: String,
 }
 
+pub struct GetVkResponse {
+    pub vk: String,
+    pub error: Option<String>,
+}
+
 pub struct ProveRequest {
     pub circuit_type: CircuitType,
     pub circuit_version: String,