Drupal 7 to Drupal 9 through web browser upgrade - "files do no exist"

Question

I am using the Migrate Drupal UI module to upgrade a simple Drupal 7 site to Drupal 9 using the web browser upgrade form.

I am having an issue where when the upgrade runs it says the files do not exist.

Here is what I have tried:

1. Run the upgrade through the form with correct database credentials and with the source path sites/default/files and this is what the error looks like

SOURCE ID 6017: d7_file:uri:file_copy: File 'sites/default/files/folder-name/file-name.zip' does not exist

2. Before running the upgrade, manually put the files in the sites/default/files folder on the blank drupal 9 site using FTP, run it and this is what the error looks like.

SOURCE ID 6017: d7_file:uri:file_copy: File 'sites/default/files//folder-name/file-name.zip' does not exist

Some other important info: -the file types are zip files -note with the second attempt a double slash appears in front of the folder