diff --git a/lib/utils/blob-service.js b/lib/utils/blob-service.js
--- a/lib/utils/blob-service.js
+++ b/lib/utils/blob-service.js
@@ -5,9 +5,16 @@
 
 import { toBase64URL } from './base64.js';
 import { replacePathParams, type URLPathParams } from './url-utils.js';
+import { assertWithValidator } from './validation-utils.js';
 import type { BlobServiceHTTPEndpoint } from '../facts/blob-service.js';
 import blobServiceConfig from '../facts/blob-service.js';
-import type { BlobHashAndHolder } from '../types/holder-types.js';
+import {
+  type BlobInfo,
+  type AssignMultipleHoldersRequest,
+  type RemoveMultipleHoldersRequest,
+  assignMultipleHoldersResponseValidator,
+  removeMultipleHoldersResponseValidator,
+} from '../types/blob-service-types.js';
 
 const BLOB_SERVICE_URI_PREFIX = 'comm-blob-service://';
 
@@ -113,19 +120,19 @@
 }
 
 async function assignMultipleHolders(
-  holders: $ReadOnlyArray<{ +blobHash: string, +holder: string }>,
+  holders: $ReadOnlyArray<BlobInfo>,
   headers: { [string]: string },
 ): Promise<
   | { +result: 'success' }
   | { +result: 'error', +status: number, +statusText: string }
   | {
-      +failedRequests: $ReadOnlyArray<{
-        +blobHash: string,
-        +holder: string,
-      }>,
+      +failedRequests: $ReadOnlyArray<BlobInfo>,
       +result: 'failed_requests',
     },
 > {
+  const requestBody: AssignMultipleHoldersRequest = {
+    requests: holders,
+  };
   const assignMultipleHoldersResponse = await fetch(
     makeBlobServiceEndpointURL(
       blobServiceConfig.httpEndpoints.ASSIGN_MULTIPLE_HOLDERS,
@@ -133,9 +140,7 @@
     {
       method: blobServiceConfig.httpEndpoints.ASSIGN_MULTIPLE_HOLDERS.method,
       headers: { ...headers, 'Content-Type': 'application/json' },
-      body: JSON.stringify({
-        requests: holders,
-      }),
+      body: JSON.stringify(requestBody),
     },
   );
 
@@ -144,7 +149,11 @@
     return { result: 'error', status, statusText };
   }
 
-  const { results } = await assignMultipleHoldersResponse.json();
+  const responseJson = await assignMultipleHoldersResponse.json();
+  const { results } = assertWithValidator(
+    responseJson,
+    assignMultipleHoldersResponseValidator,
+  );
   const failedRequests = results
     .filter(result => !result.success)
     .map(({ blobHash, holder }) => ({ blobHash, holder }));
@@ -157,7 +166,7 @@
 }
 
 async function removeMultipleHolders(
-  holders: $ReadOnlyArray<BlobHashAndHolder>,
+  holders: $ReadOnlyArray<BlobInfo>,
   headers: { [string]: string },
   instantDelete?: boolean,
 ): Promise<
@@ -165,9 +174,13 @@
   | { +result: 'error', +status: number, +statusText: string }
   | {
       +result: 'failed_requests',
-      +failedRequests: $ReadOnlyArray<BlobHashAndHolder>,
+      +failedRequests: $ReadOnlyArray<BlobInfo>,
     },
 > {
+  const requestBody: RemoveMultipleHoldersRequest = {
+    requests: holders,
+    instantDelete: !!instantDelete,
+  };
   const response = await fetch(
     makeBlobServiceEndpointURL(
       blobServiceConfig.httpEndpoints.REMOVE_MULTIPLE_HOLDERS,
@@ -175,10 +188,7 @@
     {
       method: blobServiceConfig.httpEndpoints.REMOVE_MULTIPLE_HOLDERS.method,
       headers: { ...headers, 'Content-Type': 'application/json' },
-      body: JSON.stringify({
-        requests: holders,
-        instantDelete: !!instantDelete,
-      }),
+      body: JSON.stringify(requestBody),
     },
   );
 
@@ -187,7 +197,12 @@
     return { result: 'error', status, statusText };
   }
 
-  const { failedRequests } = await response.json();
+  const responseJson = await response.json();
+  const { failedRequests } = assertWithValidator(
+    responseJson,
+    removeMultipleHoldersResponseValidator,
+  );
+
   if (failedRequests.length !== 0) {
     return { result: 'failed_requests', failedRequests };
   }