Need Help to find out hash type

Hi!

I captured HTTP POST data. The posted data is verified with a X-Signature-Header.

If i resend the same data, i got a success message.
If i change the data i got a message from Server {"status":"INVALID_AUTH_SIGNATURE"}

Here is an example Signature Header:
"X-Signature: 6b3d91b6118ebbd6ba6e1360f782c5c6"

I want to find out which hash-type is used to change the content of data, calculate the signature and create my own posts.

I have the posted data in a file and know the signature - Can you help me a hint how can i realize my plan?


Thank you and so long,
josen