error at installing app

I have created a site and a new app named ‘test1’.
When I try to install it to the site this error comes "Could not find app “test1”.
Also I saw that in the file apps.txt only erpnext and frappe are present.
In the apps folder, there is a ‘test1’ folder after creating it.

Is there anything else I should configure?

Thank you.

Your app might not be created properly, please try to recreate it and install again

ok, I have tried with two others, named ‘test2’ and ‘test3’ and saw the same behavior…
I also added the app, for example ‘test1’ to apps.txt which causes the error
“ModuleNotFoundError: No module named ‘test1’”