diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ea2c7dc9ca..c8cc1216528 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Gateway: raise WS payload/buffer limits so 5,000,000-byte image attachments work reliably. (#14486) Thanks @0xRaini.
 - Cron: use requested `agentId` for isolated job auth resolution. (#13983) Thanks @0xRaini.
 - Cron: prevent cron jobs from skipping execution when `nextRunAtMs` advances. (#14068) Thanks @WalterSumbon.
 - Cron: pass `agentId` to `runHeartbeatOnce` for main-session jobs. (#14140) Thanks @ishikawa-pro.
diff --git a/src/gateway/chat-attachments.ts b/src/gateway/chat-attachments.ts
index 0ff3181ee8a..4a4308b57ae 100644
--- a/src/gateway/chat-attachments.ts
+++ b/src/gateway/chat-attachments.ts
@@ -64,7 +64,7 @@ export async function parseMessageWithAttachments(
   attachments: ChatAttachment[] | undefined,
   opts?: { maxBytes?: number; log?: AttachmentLog },
 ): Promise<ParsedMessageWithImages> {
-  const maxBytes = opts?.maxBytes ?? 5_000_000; // 5 MB
+  const maxBytes = opts?.maxBytes ?? 5_000_000; // decoded bytes (5,000,000)
   const log = opts?.log;
   if (!attachments || attachments.length === 0) {
     return { message, images: [] };
diff --git a/src/gateway/server-constants.ts b/src/gateway/server-constants.ts
index 996ea63585b..03107331fed 100644
--- a/src/gateway/server-constants.ts
+++ b/src/gateway/server-constants.ts
@@ -1,5 +1,5 @@
-export const MAX_PAYLOAD_BYTES = 512 * 1024; // cap incoming frame size
-export const MAX_BUFFERED_BYTES = 1.5 * 1024 * 1024; // per-connection send buffer limit
+export const MAX_PAYLOAD_BYTES = 8 * 1024 * 1024; // cap incoming frame size (~8 MiB; fits ~5,000,000 decoded bytes as base64 + JSON overhead)
+export const MAX_BUFFERED_BYTES = 16 * 1024 * 1024; // per-connection send buffer limit (2x max payload)
 
 const DEFAULT_MAX_CHAT_HISTORY_MESSAGES_BYTES = 6 * 1024 * 1024; // keep history responses comfortably under client WS limits
 let maxChatHistoryMessagesBytes = DEFAULT_MAX_CHAT_HISTORY_MESSAGES_BYTES;
diff --git a/src/slack/monitor/message-handler/prepare.sender-prefix.test.ts b/src/slack/monitor/message-handler/prepare.sender-prefix.test.ts
index 8f8c7a3386b..30cfdc1ef9d 100644
--- a/src/slack/monitor/message-handler/prepare.sender-prefix.test.ts
+++ b/src/slack/monitor/message-handler/prepare.sender-prefix.test.ts
@@ -44,7 +44,7 @@ describe("prepareSlackMessage sender prefix", () => {
       ackReactionScope: "off",
       mediaMaxBytes: 1000,
       removeAckAfterReply: false,
-      logger: { info: vi.fn() },
+      logger: { info: vi.fn(), warn: vi.fn() },
       markMessageSeen: () => false,
       shouldDropMismatchedSlackEvent: () => false,
       resolveSlackSystemEventSessionKey: () => "agent:main:slack:channel:c1",
@@ -123,7 +123,7 @@ describe("prepareSlackMessage sender prefix", () => {
       ackReactionScope: "off",
       mediaMaxBytes: 1000,
       removeAckAfterReply: false,
-      logger: { info: vi.fn() },
+      logger: { info: vi.fn(), warn: vi.fn() },
       markMessageSeen: () => false,
       shouldDropMismatchedSlackEvent: () => false,
       resolveSlackSystemEventSessionKey: () => "agent:main:slack:channel:c1",