diff --git a/packages/runtime/client/rest/src/contract/endpoints/singleton.ts b/packages/runtime/client/rest/src/contract/endpoints/singleton.ts
index f870ad2e..b5f4046d 100644
--- a/packages/runtime/client/rest/src/contract/endpoints/singleton.ts
+++ b/packages/runtime/client/rest/src/contract/endpoints/singleton.ts
@@ -14,12 +14,14 @@ import {
   ContractIdGuard,
   HexTransactionWitnessSet,
   TextEnvelope,
+  TextEnvelopeGuard,
   transactionWitnessSetTextEnvelope,
 } from "@marlowe.io/runtime-core";
 
 import { ContractDetails, ContractDetailsGuard } from "../details.js";
 import { ContractId } from "@marlowe.io/runtime-core";
 import { unsafeEither, unsafeTaskEither } from "@marlowe.io/adapter/fp-ts";
+import { assertGuardEqual, proxy } from "@marlowe.io/adapter/io-ts";
 
 export type GET = (
   contractId: ContractId
@@ -65,7 +67,20 @@ export type PUT = (
   hexTransactionWitnessSet: HexTransactionWitnessSet
 ) => TE.TaskEither<Error, void>;
 
-export const submitContractViaAxios =
+export interface SubmitContractRequest {
+  contractId: ContractId;
+  txEnvelope: TextEnvelope;
+}
+
+export const SubmitContractRequestGuard = assertGuardEqual(
+  proxy<SubmitContractRequest>(),
+  t.type({
+    contractId: ContractIdGuard,
+    txEnvelope: TextEnvelopeGuard,
+  })
+);
+
+export const submitContract =
   (axiosInstance: AxiosInstance) =>
   (contractId: ContractId, envelope: TextEnvelope) =>
     axiosInstance
diff --git a/packages/runtime/client/rest/src/index.ts b/packages/runtime/client/rest/src/index.ts
index 1f6715d4..1134604d 100644
--- a/packages/runtime/client/rest/src/index.ts
+++ b/packages/runtime/client/rest/src/index.ts
@@ -34,7 +34,6 @@ import {
   HexTransactionWitnessSet,
   WithdrawalId,
 } from "@marlowe.io/runtime-core";
-import { submitContractViaAxios } from "./contract/endpoints/singleton.js";
 import { ContractDetails } from "./contract/details.js";
 import { TransactionDetails } from "./contract/transaction/details.js";
 import { ItemRange } from "./pagination.js";
@@ -165,10 +164,7 @@ export interface RestClient {
    * Submits a signed contract creation transaction
    * @see {@link https://docs.marlowe.iohk.io/api/submit-contract-to-chain | The backend documentation}
    */
-  submitContract(
-    contractId: ContractId,
-    txEnvelope: TextEnvelope
-  ): Promise<void>;
+  submitContract(request: Contract.SubmitContractRequest): Promise<void>;
 
   /**
    * Gets a paginated list of  {@link contract.TxHeader } for a given contract.
@@ -495,7 +491,7 @@ export function mkRestClient(
         if (result._tag === "Left") {
           throw new InvalidArgumentError(
             result.left,
-            `Invalid argument to getContractSourceAdjacency(${request})`
+            `Invalid argument to getNextStepsForContract(${request})`
           );
         } else {
           const test: typeof request = result.right;
@@ -503,8 +499,20 @@ export function mkRestClient(
       }
       return Next.getNextStepsForContract(axiosInstance)(request);
     },
-    submitContract(contractId, txEnvelope) {
-      return submitContractViaAxios(axiosInstance)(contractId, txEnvelope);
+    submitContract(request) {
+      if (strict) {
+        const result = Contract.SubmitContractRequestGuard.decode(request);
+        if (result._tag === "Left") {
+          throw new InvalidArgumentError(
+            result.left,
+            `Invalid argument to submitContract(${request})`
+          );
+        } else {
+          const test: typeof request = result.right;
+        }
+      }
+      const { contractId, txEnvelope } = request;
+      return Contract.submitContract(axiosInstance)(contractId, txEnvelope);
     },
     getTransactionsForContract(contractId, range) {
       return unsafeTaskEither(
diff --git a/packages/runtime/lifecycle/src/generic/contracts.ts b/packages/runtime/lifecycle/src/generic/contracts.ts
index 9ca7ea26..0c1fe7c7 100644
--- a/packages/runtime/lifecycle/src/generic/contracts.ts
+++ b/packages/runtime/lifecycle/src/generic/contracts.ts
@@ -149,10 +149,10 @@ const createContract =
       buildCreateContractTxResponse.tx.cborHex
     );
 
-    await restClient.submitContract(
+    await restClient.submitContract({
       contractId,
-      transactionWitnessSetTextEnvelope(hexTransactionWitnessSet)
-    );
+      txEnvelope: transactionWitnessSetTextEnvelope(hexTransactionWitnessSet),
+    });
     return [contractId, contractIdToTxId(contractId)];
   };