no, because you didnt show any code. read SSCCE

working as expected. Return status as 200 and content in JSON

print CGI::header({type => 'application/json', status => '200 OK', 

print "$json_encoded_data";
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Not working code, Returning as 400 status but content type is html only.

print CGI::header({type => 'application/json', status => '400 Bad Requ
+est', 

print "$json_encoded_data";
[download]

Let's look at the RFC for HTTP status code 400:

6.5.1.  400 Bad Request

   The 400 (Bad Request) status code indicates that the server cannot 
+or
   will not process the request due to something that is perceived to 
+be
   a client error (e.g., malformed request syntax, invalid request
   message framing, or deceptive request routing).
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Basically, "400" code tells the server that you did not properly understood the request or refused to parse it. Depending on your webserver software, it may choose to interpret that to mean "i could not make sense of this, send the default error page".

Are you SURE this is actually the error code you want to use? It basically means "i did not understand your request at all".

Unless the client sent complete garbage, in all likelyhood there is a HTTP status code from the 4xx group that will fit better. Take a look.

perl -e 'use Crypt::Digest::SHA256 qw[sha256_hex]; print substr(sha256_hex("the Answer To Life, The Universe And Everything"), 6, 2), "\n";'

Your code has syntax errors and does not compile. Please help us help you by making your problem reproducible.

What server are you using to host this service? How is it set up? Which exact response (including all headers) are you receiving in both cases?