Module development and code questions

I'm working on a module to import a Excel file and using PhpSpreadsheet class. Now, if my uploaded file is out of public://, I have no problems at all importing it. But if I have it in public://, I get PHP message: Uncaught PHP Exception InvalidArgumentException: "File "" does not exist." at File.php line 137. Line 137 throws an exception if the file is not a file, but dpm says it is. What am I doing wrong? Below is my code:

Hello Friends,

I am new to Drupal development.

I have been asked to develop a custom module that utilizes a master-detail approach for business listings. The listings need to be queried from a external database (not drupals native one)

The module should also allow for full CRUD of listings, as well as implement search/filter functionality on the master listings page (list of listings) 

At the moment I have 3 main routes:

/all-listings

/add-listing

/listing-detail{id}

I am new to Drupal development. I have been tasked with creating a custom Drupal 8 listings website. You should be able to add listings, search listing and view them via a master detail approach. The listings need to be queried from a external database (not Drupals native one).

My solution to this was to create a custom module named business_listings.

I am currently storing the listings in a external database in a table called business_listings

Hello Friends,

I am new to Drupal development. I have been tasked with creating a custom Drupal 8 listings website. You should be able to add listings, search listing and view them via a master detail approach. The listings need to be queried from a external database (not Drupals native one).

My solution to this was to create a custom module named business_listings.

I am currently storing the listings in a external database in a table called business_listings

Hello Friends,

I am new to Drupal development. I have been tasked with creating a custom Drupal 8 listings website. You should be able to add listings, search listing and view them via a master detail approach. The listings need to be queried from a external database (not Drupals native one).

My solution to this was to create a custom module named business_listings.

I am currently storing the listings in a external database in a table called business_listings

Hello Friends,

I am trying to connect to and query a external/second database in my custom Drupal module, I believe I am very close to achieving this.

I have added the external database to settings.php :