DKIM Fail on phplist selfhosted

Hello, I am using phplist (self hosted) on my shared cpanel hosting.
I am trying to send emails using external SMTP connection.
NOTE: The SMTP service I am using does not sign the messages through DKIM. They, instead forward host/MTA dkim settings and let host/MTA sign the message.

Following is my setup:

  1. Using Cpanel shared hosting to host domain’s DNS.
  2. Same cpanel to host phplist.
  3. Enabled SMTP connection under phplist/config.php and phplist/config_extended.php
  4. DKIM plugin for signing messages in phplist.

Now, I am using the same default._domainkey selector which is provided by cpanel in phplist->dkimsettings
Also, cpnale has provided the private key which I have put in the dkim plugin’s private key section. mentioned “default” as dkim selector too.

When I send emails using this configuration, I get the following error from gmail:
dkim=neutral (body hash did not verify)

Kindly suggest solution to this issue.