Custom login page and custom membership provider sharepoint 2016

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SharePoint2016

Dear Friend,
I have create a custom login page with Custom membership provider. In membership provider there is a function name validateUser(string loginname, String password)
{
SqlDataReader rdr = cmd.ExecuteReader();

if (rdr.HasRows)
{
while (rdr.Read())
{
int RetryAttempts = Convert.ToInt32(rdr["RetryAttempts"]);
if (Convert.ToBoolean(rdr["AccountLocked"]))
{
LblMessage.Text = "Account Locked, Please contact to Administrator";
ISAuthenticated = false;
}
else if (RetryAttempts > 0)
{
int AttemptsLeft = (4 - RetryAttempts);

//LblMessage.Text = "Invalid User Name and/OR password" + AttemptsLeft.ToString() + " attemp(s) left";
ISAuthenticated = false;
}
else if (Convert.ToBoolean(rdr["Authenticated"]))
{

ISAuthenticated = true;
}

}

}
else
{
//LblMessage.Text = "you are not autharised user. Please Register First";
ISAuthenticated = false;
}
}

My problem is that I am unable to assign text value in Label (LblMessage) which is on login page from membership provider class. please help

What I have tried:

Claims Walkthrough: Creating Forms-Based Authentication for Claims-Based SharePoint 2010 Web Applications Using Custom Membership and Role Providers[^]