diff --git a/legacy/readme.md b/legacy/readme.md
index 6a46fea7..473afb55 100644
--- a/legacy/readme.md
+++ b/legacy/readme.md
@@ -327,7 +327,7 @@ These libraries work with email + password accounts (e.g., they do not support a
 
 Alternatively, you can manually get an `accessToken` by logging in to the ChatGPT webapp and then opening `https://chat.openai.com/api/auth/session`, which will return a JSON object containing your `accessToken` string.
 
-Access tokens last for ~8 hours.
+Access tokens last for days.
 
 **Note**: using a reverse proxy will expose your access token to a third-party. There shouldn't be any adverse effects possible from this, but please consider the risks before using this method.
 
diff --git a/legacy/src/chatgpt-unofficial-proxy-api.ts b/legacy/src/chatgpt-unofficial-proxy-api.ts
index 6fe2fa6c..87eae0a1 100644
--- a/legacy/src/chatgpt-unofficial-proxy-api.ts
+++ b/legacy/src/chatgpt-unofficial-proxy-api.ts
@@ -4,6 +4,7 @@ import { v4 as uuidv4 } from 'uuid'
 import * as types from './types'
 import { fetch as globalFetch } from './fetch'
 import { fetchSSE } from './fetch-sse'
+import { isValidUUIDv4 } from './utils'
 
 export class ChatGPTUnofficialProxyAPI {
   protected _accessToken: string
@@ -97,6 +98,30 @@ export class ChatGPTUnofficialProxyAPI {
     text: string,
     opts: types.SendMessageBrowserOptions = {}
   ): Promise<types.ChatMessage> {
+    if (!!opts.conversationId !== !!opts.parentMessageId) {
+      throw new Error(
+        'ChatGPTUnofficialProxyAPI.sendMessage: conversationId and parentMessageId must both be set or both be undefined'
+      )
+    }
+
+    if (opts.conversationId && !isValidUUIDv4(opts.conversationId)) {
+      throw new Error(
+        'ChatGPTUnofficialProxyAPI.sendMessage: conversationId is not a valid v4 UUID'
+      )
+    }
+
+    if (opts.parentMessageId && !isValidUUIDv4(opts.parentMessageId)) {
+      throw new Error(
+        'ChatGPTUnofficialProxyAPI.sendMessage: parentMessageId is not a valid v4 UUID'
+      )
+    }
+
+    if (opts.messageId && !isValidUUIDv4(opts.messageId)) {
+      throw new Error(
+        'ChatGPTUnofficialProxyAPI.sendMessage: messageId is not a valid v4 UUID'
+      )
+    }
+
     const {
       conversationId,
       parentMessageId = uuidv4(),
diff --git a/legacy/src/utils.ts b/legacy/src/utils.ts
new file mode 100644
index 00000000..c849d5ce
--- /dev/null
+++ b/legacy/src/utils.ts
@@ -0,0 +1,6 @@
+const uuidv4Re =
+  /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i
+
+export function isValidUUIDv4(str: string): boolean {
+  return str && uuidv4Re.test(str)
+}