diff --git a/changes/10732.fix.md b/changes/10732.fix.md
new file mode 100644
index 00000000000..cb27913b649
--- /dev/null
+++ b/changes/10732.fix.md
@@ -0,0 +1 @@
+Fix AttributeError in v2 login CLI when server returns a string in the data field (BA-5559)
diff --git a/src/ai/backend/client/cli/v2/login_cmd.py b/src/ai/backend/client/cli/v2/login_cmd.py
index 0a241863710..4e12ff574d0 100644
--- a/src/ai/backend/client/cli/v2/login_cmd.py
+++ b/src/ai/backend/client/cli/v2/login_cmd.py
@@ -48,15 +48,30 @@ async def _run() -> None:
             async with client.session.post(login_url, json=payload) as resp:
                 data = await resp.json()
 
+            def _get_details(resp_data: dict[str, Any]) -> str:
+                raw = resp_data.get("data")
+                if isinstance(raw, dict):
+                    details = raw.get("details")
+                    if details:
+                        return str(details)
+                elif raw:
+                    return str(raw)
+                # Handle RFC 7807 problem responses (e.g., {"type": ..., "title": ...})
+                if "title" in resp_data:
+                    return str(resp_data["title"])
+                return "Unknown error"
+
             if not data.get("authenticated"):
-                if data.get("data", {}).get("details") == "OTP not provided":
+                details = _get_details(data)
+
+                if details == "OTP not provided":
                     otp = input("One-time Password: ")
                     payload["otp"] = otp.strip()
                     async with client.session.post(login_url, json=payload) as resp:
                         data = await resp.json()
 
             if not data.get("authenticated"):
-                details = data.get("data", {}).get("details", "Unknown error")
+                details = _get_details(data)
                 click.echo(click.style(f"Login failed: {details}", fg="red"))
                 raise SystemExit(1)