CRM 2016 IFD - error 404

Hi,

We are finishing our IFD deployment.

Internally when I access https://crmint.domain.com it´s request authentication (ok) and then redirect to

https://crmint.domain.com/Orgname/main.aspx

Externally I access https://crmext.domain.com it´s redirects to IFD Forms Authentication (ok) and then NOT redirect and I receive a 404 error (page not found)

Doing some tests if I put manually after the login https://crmext.domain.com/main.aspx I can access with successful , yes without Orgname

Now my question is, Why it is not redirecting to main.aspx and how I can customize or correct this.

Thanks in advance.