How to get permission to download files?

Question

Google

We are setting up a google drive api for our crm system and have run into some problems.
I'll try to describe the problem one by one
1. Created a user admin.google.com
2. Created a service account - general credentials
3. Made authorization successful.
4. Uploaded files - everything works.
The problem is that there are no rights to download these files.
Tried using 2 methods to download files:
a) $downloadUrl = $file->getWebContentLink(); - error 403 - no rights
b) $downloadUrl = $file->getDownloadUrl(); return $httpRequest->getResponseBody(); - returns the content of files.
I read in google that you need to give permissions for the client id, and I did it ...
What could be the problem?