403 Forbidden Error while accessing appian 18.1 server URL

Hi rajesh ,

We have faced the same issue before so we have gone through below steps.

step-1: Please check the permissions on the folder. The user that is running Appian on the server should have full read, write, and execute
permissions for <APPIAN_HOME> and all sub folders and files.

After completion of the above step we can able to access the respected URL but while logging we are unable to logging into respected URL For that we removed the below lines under the file "<Appian_HOME>/ear/suite.ear/web.war/WEB-INF/web.xml" and then try again with the same credentials

Step-2:
>>>>>>>>>>>>>>>>>>>
<cookie-config>
<http-only>true</http-only>
<secure>true</secure>
</cookie-config>
<tracking-mode>COOKIE</tracking-mode>

After the above two steps we can successfully logged into respected site .

Please try above steps they may help to resolve your issue.

Thanks