diff --git a/remittance_split/README.md b/remittance_split/README.md
index 6383f3bd..9351ecc4 100644
--- a/remittance_split/README.md
+++ b/remittance_split/README.md
@@ -8,10 +8,14 @@ across spending, savings, bills, and insurance categories.
 `distribute_usdc` is the only function that moves funds. It enforces the following invariants
 in strict order before any token interaction occurs:
 
-1. **Auth first** — `from.require_auth()` is the very first operation; no state is read before
-   the caller proves authority.
-2. **Pause guard** — the contract must not be globally paused.
-3. **Owner-only** — `from` must equal the address stored as `config.owner` at initialization.
+1. **Domain-Separated Auth** — `initialize_split` uses a structured `InitializationPayload`
+   containing the network ID, contract address, owner, and nonce. This payload must be
+   explicitly signed, preventing the authorization from being replayed on different contract
+   instances or Stellar networks.
+2. **Auth first** — For other operations, `caller.require_auth()` is the very first operation;
+   no state is read before the caller proves authority.
+3. **Pause guard** — the contract must not be globally paused.
+4. **Owner-only** — `from` must equal the address stored as `config.owner` at initialization.
    Any other address is rejected with `Unauthorized`, even if it can self-authorize.
 4. **Trusted token** — `usdc_contract` must match the address pinned in `config.usdc_contract`
    at initialization time. Passing a different address returns `UntrustedTokenContract`,
diff --git a/remittance_split/src/lib.rs b/remittance_split/src/lib.rs
index 0f46fe3c..04d082c9 100644
--- a/remittance_split/src/lib.rs
+++ b/remittance_split/src/lib.rs
@@ -5,7 +5,7 @@ mod test;
 
 use soroban_sdk::{
     contract, contracterror, contractimpl, contracttype, symbol_short, token::TokenClient, vec,
-    Address, Env, Map, Symbol, Vec,
+    Address, BytesN, Env, IntoVal, Map, Symbol, Vec,
 };
 
 // Event topics
@@ -359,7 +359,7 @@ impl RemittanceSplit {
         // Emit admin transfer event for audit trail
         env.events().publish(
             (symbol_short!("split"), symbol_short!("adm_xfr")),
-            (current_upgrade_admin, new_admin.clone()),
+            (current_upgrade_admin.clone(), new_admin.clone()),
         );
 
         Ok(())
@@ -440,7 +440,20 @@ impl RemittanceSplit {
         bills_percent: u32,
         insurance_percent: u32,
     ) -> Result<bool, RemittanceSplitError> {
-        owner.require_auth();
+        let payload = SplitAuthPayload {
+            domain_id: symbol_short!("init"),
+            network_id: env.ledger().network_id(),
+            contract_addr: env.current_contract_address(),
+            owner_addr: owner.clone(),
+            nonce_val: nonce,
+            usdc_contract: usdc_contract.clone(),
+            spending_percent,
+            savings_percent,
+            bills_percent,
+            insurance_percent,
+        };
+        owner.require_auth_for_args(vec![&env, payload.into_val(&env)]);
+
         Self::require_not_paused(&env)?;
         Self::require_nonce(&env, &owner, nonce)?;
 
diff --git a/remittance_split/src/test.rs b/remittance_split/src/test.rs
index f3db8645..f5a69751 100644
--- a/remittance_split/src/test.rs
+++ b/remittance_split/src/test.rs
@@ -5,7 +5,7 @@ use soroban_sdk::{
     testutils::storage::Instance as StorageInstance,
     testutils::{Address as AddressTrait, Events, Ledger, LedgerInfo},
     token::{StellarAssetClient, TokenClient},
-    Address, Env, Symbol, TryFromVal,
+    Address, Env, Symbol, TryFromVal, TryIntoVal,
 };
 
 // ---------------------------------------------------------------------------
@@ -67,6 +67,44 @@ fn setup_initialized_split<'a>(
 // initialize_split
 // ---------------------------------------------------------------------------
 
+#[test]
+fn test_initialize_split_domain_separated_auth() {
+    let env = Env::default();
+    env.mock_all_auths();
+    let contract_id = env.register_contract(None, RemittanceSplit);
+    let client = RemittanceSplitClient::new(&env, &contract_id);
+    let owner = Address::generate(&env);
+    let token_admin = Address::generate(&env);
+    let token_id = setup_token(&env, &token_admin, &owner, 0);
+
+    client.initialize_split(&owner, &0, &token_id, &50, &30, &15, &5);
+
+    // Verify that the authorization includes the full domain-separated payload
+    let auths = env.auths();
+    assert_eq!(auths.len(), 1);
+    
+    // The auths captured by mock_all_auths record what was authorized.
+    // In our case, the contract calls owner.require_auth_for_args(payload).
+    let (address, auth_invocation) = auths.get(0).unwrap();
+    assert_eq!(address, owner);
+    
+    // The top-level invocation from mock_all_auths for require_auth_for_args
+    // will have the authorized arguments.
+    let payload_val = auth_invocation.args.get(0).unwrap();
+    let payload: SplitAuthPayload = payload_val.try_into_val(&env).unwrap();
+    
+    assert_eq!(payload.domain_id, symbol_short!("init"));
+    assert_eq!(payload.network_id, env.ledger().network_id());
+    assert_eq!(payload.contract_addr, contract_id);
+    assert_eq!(payload.owner_addr, owner);
+    assert_eq!(payload.nonce_val, 0);
+    assert_eq!(payload.usdc_contract, token_id);
+    assert_eq!(payload.spending_percent, 50);
+    assert_eq!(payload.savings_percent, 30);
+    assert_eq!(payload.bills_percent, 15);
+    assert_eq!(payload.insurance_percent, 5);
+}
+
 #[test]
 fn test_initialize_split_succeeds() {
     let env = Env::default();