Error while installing GeoPandas using pipenv "proj executable not found"

I tried to install GeoPandas using the following command:

pipenv install geopandas

But I had an error:

Installing geopandas…
Error:  An error occurred while installing geopandas!
Error text: Collecting geopandas
Using cached geopandas-0.9.0-py2.py3-none-any.whl (994 kB)
Collecting pyproj>=2.2.0
Using cached pyproj-3.0.1.tar.gz (168 kB)
Installing build dependencies: started
Installing build dependencies: finished with status 'done'
Getting requirements to build wheel: started
Getting requirements to build wheel: finished with status 'error'

ERROR: Command errored out with exit status 1:
 command: 'C:Usersmm.virtualenvsPython_Scripts-6r4YuOo9Scriptspython.exe' 

‘C:Usersmm.virtualenvsPython_Scripts-6r4YuOo9libsite-
packagespip_vendorpep517_in_process.py’ get_requires_for_build_wheel
‘C:UsersmmAppDataLocalTemptmpojq98inx’
cwd: C:UsersmmAppDataLocalTemppip-install-xw_50bxmpyproj
Complete output (1 lines):
proj executable not found. Please set the PROJ_DIR variable. For more information see:
https://pyproj4.github.io/pyproj/stable/installation.html
—————————————-
ERROR: Command errored out with exit status 1: ‘C:Usersmm.virtualenvsPython_Scripts-
6r4YuOo9Scriptspython.exe’ ‘C:Usersmm.virtualenvsPython_Scripts-6r4YuOo9libsite-
packagespip_vendorpep517_in_process.py’ get_requires_for_build_wheel
‘C:UsersmmAppDataLocalTemptmpojq98inx’ Check the logs for full command output.

    Installation Failed

What should I do?