LDAP authentication not successful from azure server machine

See more:

C#

LDAP

Hi All,

I am migrating my Intranet application to Azure.I am struggling with LDAP authentication. Please take a look and help.
--
We have running an Intranet Application from On-Prem server 'A'. LDAP authenticaion successfully done at AD server 'B'. Both are in Domain 'X'

Usually, employees are logging in with the user credentials 'USR0123' & password. Once, their credential check is succeeded, then the site will open the HOME page.
My LDAP query is "LDAP://DomainX.local/DC=DomainX,DC=local". Which is currently working fine in 'DomainX'.

Now, we are migrating the Intranet application to Azure.
An Azure server 'C' created to have the above said 'Intranet application and deployed.
The server 'C' and the server 'B' are trusted between them for LDAP authentication purpose.

The Problem is:
When the 'USR0123' logged into the 'Intranet Application from the server 'A' or 'C', it throws an error as below.
"Login failed for user 'aa.adminuser'".
Actually, the user keyed his user id 'USR0123' only.
But, it shows the failure message for *azure user id (aa.adminuser).
For every user it's showing the same error.

As, I am not familiar with LDAP in deep.
Please help me in
- what i need to do with my existing LDAP query.

Thanks.

What I have tried:

1. I have changed "LDAP://DomainX.local/DC=DomainX,DC=local" to
"LDAP://DCServer.DomainX.local/DC=DomainX,DC=local"
2. Network team checked the ports and TCP connections. TcpTestSucceeded.