This issue can happen if a Web server returns a form with a http 403 error code. The Access Gateway, by default, returns its own custom error pages. Hence, this prevents the Form Fill feature to work. To workaround, go to Access Gateway > Advanced Options, enter ProxyErrorOverride off > click OK.
While installing the NMAS SAML method in an external user store, DN is added as Provider ID instead of the metadata URL.
To resolve this issue, perform the following steps:
Log in to the Administration Console which has the external user store.
Go to Roles and Tasks > NMAS > NMAS Login Methods > SAML Assertion > Affiliates.
Select the respective Affiliate and change the provider ID to the identity provider metadata URL. For example, https://www.trunk2.com:8443/nidp/idff/metadata.