diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -397,7 +397,7 @@
 ): string {
   let pendingThreadKey;
   if (sourceMessageID && threadTypeIsThick(threadType)) {
-    pendingThreadKey = `thick_sidebar/${sourceMessageID}`;
+    pendingThreadKey = `dm_sidebar/${sourceMessageID}`;
   } else if (sourceMessageID) {
     pendingThreadKey = `sidebar/${sourceMessageID}`;
   } else {
@@ -425,7 +425,7 @@
 
   const [threadTypeString, threadKey] = pendingThreadIDMatches[1].split('/');
   let threadType;
-  if (threadTypeString === 'thick_sidebar') {
+  if (threadTypeString === 'dm_sidebar') {
     threadType = threadTypes.THICK_SIDEBAR;
   } else if (threadTypeString === 'sidebar') {
     threadType = threadTypes.SIDEBAR;
@@ -434,7 +434,7 @@
   }
 
   const threadTypeStringIsSidebar =
-    threadTypeString === 'sidebar' || threadTypeString === 'thick_sidebar';
+    threadTypeString === 'sidebar' || threadTypeString === 'dm_sidebar';
   const memberIDs = threadTypeStringIsSidebar ? [] : threadKey.split('+');
   const sourceMessageID = threadTypeStringIsSidebar ? threadKey : null;
   return {
diff --git a/lib/shared/thread-utils.test.js b/lib/shared/thread-utils.test.js
--- a/lib/shared/thread-utils.test.js
+++ b/lib/shared/thread-utils.test.js
@@ -36,7 +36,7 @@
     memberIDs: [],
     sourceMessageID: '12345',
   };
-  expect(parsePendingThreadID('pending/thick_sidebar/12345')).toStrictEqual(
+  expect(parsePendingThreadID('pending/dm_sidebar/12345')).toStrictEqual(
     thickSidebarResult,
   );
 
@@ -210,6 +210,6 @@
   it('should return correct ID from thick sidebar input', () => {
     expect(
       getPendingThreadID(threadTypes.THICK_SIDEBAR, [], '12345'),
-    ).toStrictEqual('pending/thick_sidebar/12345');
+    ).toStrictEqual('pending/dm_sidebar/12345');
   });
 });
diff --git a/lib/utils/validation-utils.js b/lib/utils/validation-utils.js
--- a/lib/utils/validation-utils.js
+++ b/lib/utils/validation-utils.js
@@ -112,7 +112,7 @@
   '[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}';
 const idSchemaRegex = `(?:(?:[0-9]+|${uuidRegex})\\|)?(?:[0-9]+|${uuidRegex})`;
 
-const pendingThreadIDRegex = `pending/(type[0-9]+/[0-9]+(\\+[0-9]+)*|(sidebar|thick_sidebar)/${idSchemaRegex})`;
+const pendingThreadIDRegex = `pending/(type[0-9]+/[0-9]+(\\+[0-9]+)*|(sidebar|dm_sidebar)/${idSchemaRegex})`;
 const thickThreadIDRegex: RegExp = new RegExp(`^${uuidRegex}$`);
 
 const chatNameMaxLength = 191;