Find Real Testers can sometimes be challenging because Google has made its policies very strict. My recommendation is to create your own testing team rather than manually adding emails or using external services.

Read more about Testing: https://medium.com/@banrossyn/20-testers-google-play-5361008bc24b

Instead of spending money on services from platforms like Fiverr or Upwork, it’s better to build your own testing group. This way, you’re not just getting testers for a single app, but you’ll have them available for multiple apps when needed.

Accordingly, it’s not right to manually add emails for closed testing. If you have a limited number of testers and you’re sure that all users will use the app daily, then you can use this method. Otherwise, you should use a Google group for testing.