Open httpd-vhosts.conf file (from Apache 's conf/extras directory), in your preferred text editor.

Change the virtual site's settings, into something like:

<VirtualHost *:80 *:443>
    ServerName my-site.local
    ServerAlias *.my-site.local
    DocumentRoot "C:\xampp\htdocs\my-project\public"
    SSLEngine on
    SSLCertificateFile "path/to/my-generated.cert"
    SSLCertificateKeyFile "path/to/my-generated.key"
    SetEnv APPLICATION_ENV "development"
    <Directory "C:\xampp\htdocs\my-project\public">
        Options Indexes FollowSymLinks
        AllowOverride All
        Order allow, deny
        Allow from all
    </Directory>
</VirtualHost>
But of course, generate a dummy-SSL-certificate, and change all file paths, like from "path/to/my-generated.cert" into real file addresses.
Finally, test by visiting the local site in the browser, but using http:// (without S) prefixed address; Apache should now give error like:
Bad Request
Your browser sent a request that this server could not understand.
Reason: You're speaking plain HTTP to an SSL-enabled server port.
Instead use the HTTPS scheme to access this URL, please.
                It worked like a charm, but my confusion is, why did it worked for QA, but not for DEV. Anyway, both of them works fine now. Thanks again.
– raja777m
                May 7, 2019 at 15:12
                I love how this answer gets so many upvotes when it literally tells you the same things the error message said to do.
– georgiaboy82
                Jun 20, 2019 at 17:09
                Somewhat related: I had my requests grouped in a collection, using a common url variable across all the requests.  I accidentally erased the variable name (even though the url values were still there) and got the error mentioned in the OP.
– Jesuisme
                Mar 17, 2019 at 5:10
                @Kerooker! Your comment is what saved me!  It was a copy pasted header key that had a leading space for me.
– saml
                Aug 20, 2019 at 18:59
If you get a "Could not get any response" message from Postman native apps while sending your request, open Postman Console (View > Show Postman Console), resend the request and check for any error logs in the console.
Thanks to numaanashraf
                Very helpful. I think I needed to disable the ssl certs, but I had added a bad header, and the console spelled that out for me.
– MattC
                Sep 25, 2019 at 13:33
                This pointed me in the right direction; in my case the console log gave a much clearer error than Postman did: "Error: Invalid character in header content ["Authorization"] Warning: This request did not get sent completely and might not have all the required system headers".
– Peter W
                Jan 31, 2020 at 3:50
                This should be the accepted answer since it helps you understand the underlying cause and not just guess it (e.g. "invalid character in header").
– Alexei - check Codidact
                Mar 4, 2020 at 16:29
                You may laugh, but a v7.17.0 fresh install had this at 60... If you hadn't mentioned it, I wouldn't look there for hours... Thanks!
– Koshinae
                Feb 6, 2020 at 14:50
If all above methods doesn't work check your environment variables, And make sure that the following environments are not set. If those are set and not needed by any other application remove them.
HTTP_PROXY
HTTPS_PROXY
Reference link
                Can you explain why a Proxy would be necessary to access a server on the local network that is having this problem?
– robross0606
                Feb 5, 2019 at 20:16
In postman go to setting --> proxy
And off Global Proxy Configuration
on the Use System Proxy
And go to windows host configure file
'C:\Windows\System32\drivers\etc\hosts'
Open that file in administrator mode 
And add the sub domain to hosts file
For me, it was that route that I was calling in my node server wasn't returning anything. Adding
    return res.status(200).json({
        message: 'success!',
        response: 'success!'
    });//
to the route I was calling resolved the issue.
You mentioned you are using a CER certificate.  
According to the Postman page on certificates.
Choose your client certificate file in the CRT file field. Currently, we only support the CRT format. Support for other formats (like PFX) will come soon.
The name of the extension CER, CRT doesn't make the certificate that type of certificate but, these are the excepted extensions names.
CER is an X.509 certificate in binary form, DER encoded.
CRT is a binary X.509 certificate, encapsulated in text (base-64) encoding.
You can use OpenSSL to change a CER file into a CRT file.  I have not had good luck with it but it looks like this.
  
openssl x509 -inform PEM -in certificate.cer -out certificate.crt
  
openssl x509 -inform DER -in certificate.cer -out certificate.crt
Postman for Linux Version 6.7.1 - Ubuntu 18.04 - linux 4.15.0-43-generic / x64
I had the same problem and by chance I replaced http://localhost with http://127.0.0.1 and everything worked.
My etc/hosts had the proper entries for localhost and https://localhost requests always worked as expected.
I have no clue why changing localhost for http with 127.0.0.1 solved the issue.
None of these solutions works for me. Postman is not sending any request to the server because postman is not finding the host. So, if you modify your /etc/hosts to
127.0.0.1 localhost
127.0.0.1 subdomain.localhost
It works for me.
For me the issue was that the Content-Length was too big. I placed the content of the body in NotePad++ and counted the characters and put that figure in PostMan and then it worked.
I know it does not directly answer why the op's sub-domain was not working but it might help out someone.
                The Postman returns the same error even if you send HTTP header content-encoding: gzip but the content is not gzipped. See stackoverflow.com/a/52854400/2988107
– Mišo
                May 29, 2019 at 6:00
In my case it was invisible spaces that postman didn't recognize, the above string of text renders as without spaces in postman.
I disabled SSL certificate Validation and System Proxy even tried on postman chrome extension(which is about to be deprecated), but when I downloaded and tried Insomnia and it gave those red dots in the place where those spaces were, must have gotten there during copy/paste
For anyone who experienced this issue with real domain instead of localhost and couldn't solve it using ANY OF THE ABOVE solutions.
Try changing your Network DNS (WIFI or LAN) to some other DNS. For me, I used Google DNS 8.8.8.8, 8.8.4.4 and it worked!
solution is very simple if you are using asp.net core 2 application . Inside ConfigureServices method inside  startup.cs file all this line 
services.AddMvc()
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)
                .AddJsonOptions(x => x.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);
After all the above methods like turning OFF SSL certificate verification, turning ON only Use System Proxy and removing HTTP_PROXY and HTTPS_PROXY system environment variables, it worked.
Note: Had to restart the Postman app, since the environment variables were changed.
Unchecking proxy and SSL Certificate Verification didn't work for me.
Unsetting PROXY environment variables did the trick.
export http_proxy=
export ftp_proxy=
export https_proxy=
Change to the directory where Postman is installed and then:
./Postman
In my case the (corporate) proxy was using a self-signed SSL certificate which Postman disliked. I discovered it by activating 
View->Show Postman console
and retrying the request. The console then showed the certificate error. In
Settings->General
I disabled 
SSL certificate verification.
The solution for me, as I'm using the deprecated Postman extension for Chrome, to solve this issue I had to:
Call some GET request using the Chrome Browser itself.
Wait for the error page "Your connection is not private" to appear.
Click on ADVANCED and then proceed to [url] (unsafe) link.
After this, requests through the extension itself should work.
In my case it was a misconfigured subnet. Only one of the 2 subnets in the ELB worked.
I figured this out by doing a nslookup and trying to curl the returned IPs directly. Only one worked. 
Postman just kept using the misconfigured one. 
I got the same "Could not get any response" issue because of wrong parameter in header. I fixed it by removing parameter HOST out of header. 
PS: Unfortunately, I was pushed to install the other software to get this information. It should be great to get this error message from Postman instead of getting general nonsense. 
I just experienced this error. In my case, the path was TOO LONG. So url like that gave me this error in postman (fake example)
http://127.0.0.1:5000/api/batch/upload_import_deactivate_from_ready_folder
whereas
http://127.0.0.1:5000/api/batch/upld_impt_deac_ready_folder
worked fine.
Hope it helps someone who by accident read that far...
We got this confusing error when a user accidentally copy/pasted a leading space character in an environment variable used to build the URL:
Example:
The request's URL was set to: http://{URL}/blah
The {URL} environment variable had a value of " hostname" (**notice the leading space character**)
This caused Postman to try to access http:// hostname/blah which gave this error message.