linux – DKIM Validating Signature, Result = Fail Details: Body Has Been Altered

I have 2 mail server,
Main Mail Server = Microsoft Exchange Server
Secondary Mail Server = Ubuntu Postfix only as SMTP Relay.
The Exchange Server is using Ubuntu Postfix SMTP as Smarthost,
And the problem is Exchange Server need to use thirdparty software to integrate with DKIM.
I used DKIM Exchange(https://github.com/Pro/dkim-exchange) as the third party software,
By following this tutorial https://colinwilson.uk/2017/07/19/setting-up-dkim-for-exchange-server/
But got a problem, when checking DKIM Signature on https://dkimvalidator.com/
I got an Error like this:

DKIM Information:
DKIM Signature
Message contains this DKIM Signature:
DKIM-Signature: v=1; a=rsa-sha256; d=example.com; s=default;
c=relaxed/relaxed; t=1619877233; h=from:subject:to:date:message-id;
bh=iOObCKJdXN6HiMEEGHi3hTEvUHxZe5CdQrWy7paoGeo=;
b=KHjroY6llEGwgpFXQwvTggVvN8pWkRarZfbxPMWZ3J6axLy7fngoJ7VXA/AJB9sc/N+UasENrvy
nflG8WgnKgN12Bh6VHC0xt/2M7SjtOI9CknSg3Bi0EZsYRqD5JJZqBWobNLV51sYbfT0W7KjdOkQX
i5u1sWfV4qskQKyIl48L3M9ktKyYEpZqlkr/a2iEJfVr+eMVrR8VnCbse/ccpZwEMHA5VtdWGh200
F60MITxLG0lYwZQ//RcOOjX9qTEKDxRdbRnFbvagGO7Co39bSyPw9Co6S7K+BI0tVO8Df9uV2H5ee
NqKQJQDZ50VdZLi8wQwSWCiT7gfukJUUsA1g==

Signature Information:
v= Version: 1
a= Algorithm: rsa-sha256
c= Method: relaxed/relaxed
d= Domain: example.com s= Selector: default
q= Protocol:
bh= iOObCKJdXN6HiMEEGHi3hTEvUHxZe5CdQrWy7paoGeo=
h= Signed Headers: from:subject:to:date:message-id
b= Data: KHjroY6llEGwgpFXQwvTggVvN8pWkRarZfbxPMWZ3J6axLy7fngoJ7VXA/AJB9sc/N+UasENrvy
nflG8WgnKgN12Bh6VHC0xt/2M7SjtOI9CknSg3Bi0EZsYRqD5JJZqBWobNLV51sYbfT0W7KjdOkQX
i5u1sWfV4qskQKyIl48L3M9ktKyYEpZqlkr/a2iEJfVr+eMVrR8VnCbse/ccpZwEMHA5VtdWGh200
F60MITxLG0lYwZQ//RcOOjX9qTEKDxRdbRnFbvagGO7Co39bSyPw9Co6S7K+BI0tVO8Df9uV2H5ee
NqKQJQDZ50VdZLi8wQwSWCiT7gfukJUUsA1g==

Public Key DNS Lookup
Building DNS Query for default._domainkey.example.com
Retrieved this publickey from DNS: v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAq4UV1gOKAQ+Gr9BmFSrGZbo3ll16g8itrrEwBckyGRYD2g+DKINm5fUYNUxn2bILpeh3AT2gJnbGydQNc7p02Hia1H/jnKDbvTfvnmcUQGHLQGYsnSgIJM3f+B5qrpyjfNufyrSr4L4YCBUr1o0KoN4p2p97iOr+MQiHY4sYIDPAcsaQ4zpAcxDmmSbtXbbBdYileN7Anpkm9ODJtNNNZzxH68jFI7ioVjInX8G1mWLKP4sxPoTa86R5C/zu97a0agXPusrCd1bWGKPxFhCUvJpFzdICUdLsVo9mEwbB12kpGrplYPgOb6B1YKn3iu/XBezv/8EIjG/N7+hAEz9C1wIDAQAB

Validating Signature
Result = fail
Details: body has been altered

Anyone have the solution for this? The DKIM Record is Valid but DKIM Signature is failing…