Here is a standard HTTP monitor that checks whether login page is up and working on the pool members.

[dennis@mifnt1slbgtm03:Active:Standalone] ~ # tmsh list gtm monitor https https.vpn.loginpage.statuscode.new
gtm monitor https https.vpn.loginpage.statuscode.new {
    cipherlist DEFAULT:+SHA:+3DES:+kEDH
    compatibility enabled
    defaults-from https
    destination *:*
    interval 30
    probe-timeout 5
    recv "HTTP/1.1 200 OK"
    send "GET /dana-na/auth/url_default/welcome.cgi HTTP/1.1\r\nHost: F5-healthcheck.eg.com\r\nConnection: Close\r\n\r\n"
    timeout 96
}

Now to test manually we can run a curl command from my awesome macbook pro

USFNTMNSIN9HTDD:~ lztx5g$ curl -I --header 'Host: F5-healthcheck.eg.com' https://employee.vpn.eg.com/dana-na/auth/url_default/welcome.cgi
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Date: Tue, 12 Jan 2021 22:44:24 GMT
x-frame-options: SAMEORIGIN
Pragma: no-cache
Cache-Control: no-store
Expires: -1
X-XSS-Protection: 1
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
Strict-Transport-Security: max-age=31536000

So you can see the response code is as expected with the HTTP/1.1 200 OK

I also check each pool member individually but have to add the --insecure since the SSL Certificate is bound to the FQDN employee.vpn.eg.com so the query to each pool member would like something like this

USFNTMNSIN9HTDD:~ lztx5g$ curl --insecure -I --header 'Host: F5-healthcheck.eg.com' https://192.168.91.229/dana-na/auth/url_default/welcome.cgi
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Date: Tue, 12 Jan 2021 23:03:23 GMT
x-frame-options: SAMEORIGIN
Pragma: no-cache
Cache-Control: no-store
Expires: -1
X-XSS-Protection: 1
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
Strict-Transport-Security: max-age=31536000

and you would run the same command but just change the IP address to the next pool member you want to test against.