Module not configuring

Problem/Motivation

Can't configure module to match simplesamlphp installation. When I adjust settings at admin/config/people/simplesamlphp_auth there are no changes made to simplesamlphp_auth.settings.yml - the file is not updated.

The result is "The website encountered an unexpected error. Please try again later." with an error log of

Uncaught PHP Exception SimpleSAML\\Error\\Exception: "Could not find the metadata of an IdP with entity ID '[identity as configured in simplesamlphp]" at /var/www/html/vendor/simplesamlphp/simplesamlphp/modules/saml/lib/Auth/Source/SP.php line 317

Steps to reproduce

1. Install SimpleSAMLPHP 2.0.2 base application and configure as a SP; run successful tests against my campus IDP
2. Install SimpleSAMLPHP Drupal module using composer require 'drupal/simplesamlphp_auth:^3.3' on my Drupal 9.5.3
3. Configuration instructions say "Then configure the module, making sure you point to the right directory for simplesamlphp (e.g., /var/simplesamlphp) and that you've mapped attributes that the IdP(s) will be sending." There is no place to set the directory, but I set the attributes through the console, at admin/config/people/simplesamlphp_auth. When I "Save Configuration," simplesamlphp_auth.settings.yml is not updated.