F5 https monitor receive string

Hello,

I am testing an HTTPS monitor on BIG-IP 17.1.2.

The server endpoint returns:

HTTP/1.1 200 OK when the service is healthy

HTTP/1.1 503 Service Unavailable when the service is unhealthy

This behavior has been confirmed from the F5 using:

curl 

In the HTTPS monitor, I tried the following Receive Strings:

-HTTP/1.1 200 

-200 OK

- HTTP 200

but the monitor stays DOWN.

If I use:

-ok||200

the monitor goes UP, however it also remains UP when the endpoint returns HTTP 503.

My question is:

How can I configure a standard HTTPS monitor so that it is UP only when the endpoint returns HTTP 200 and DOWN when it returns HTTP 503?

Thank you.