I told Flask how to import the application, by setting the FLASK_APP environment variable:
export FLASK_APP=microblog.py
It seems to make it !
I had the same issue. I had to re-export the FLASK_APP variable.
If you use CMD then: set FLASK_APP=microblog.py
set FLASK_APP=microblog.py
If you use PowerShell then: $env:FLASK_APP = '.\microblog.py'
$env:FLASK_APP = '.\microblog.py'
If you use Bash(Linux) then: export FLASK_APP=microblog.py
The problem is with the variable FLASK_APP
FLASK_APP