Question: The Heroku Build is returning this error when I'm trying to deploy a Django application for the past few days. The Django Code and File Structure are the same as Django's Official Documentation and Procfile is added in the root folder. Log - -----> Building on the Heroku-20 stack -----> Determining which buildpack to use for this app -----> Python app detected -----> No Python version was specified. Using the buildpack default: python-3.10.4 To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes Building wheels for collected packages: backports.zoneinfo Building wheel for backports.zoneinfo (pyproject.toml): started Building wheel for backports.zoneinfo (pyproject.toml): finished with status 'error' ERROR: Command errored out with exit status 1: command: /app/.heroku/python/bin/python /app/.heroku/python/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py build_wheel /tmp/tmpqqu_1qow cwd: /tmp/pip-install-txfn1ua9/backports-zoneinfo_a462ef61051d49e7bf54e715f78a34f1 Complete output (41 lines): running bdist_wheel running build running build_py creating build creating build/lib.linux-x86_64-3.10 creating build/lib.linux-x86_64-3.10/backports copying src/backports/__init__.py -> build/lib.linux-x86_64-3.10/backports creating build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/_zoneinfo.py -> build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/_tzpath.py -> build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/_common.py -> build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/_version.py -> build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/__init__.py -> build/lib.linux-x86_64-3.10/backports/zoneinfo running egg_info writing src/backports.zoneinfo.egg-info/PKG-INFO writing dependency_links to src/backports.zoneinfo.egg-info/dependency_links.txt writing requirements to src/backports.zoneinfo.egg-info/requires.txt writing top-level names to src/backports.zoneinfo.egg-info/top_level.txt reading manifest file 'src/backports.zoneinfo.egg-info/SOURCES.txt' reading manifest template 'MANIFEST.in' warning: no files found matching '*.png' under directory 'docs' warning: no files found matching '*.svg' under directory 'docs' no previously-included directories found matching 'docs/_build' no previously-included directories found matching 'docs/_output' adding license file 'LICENSE' adding license file 'licenses/LICENSE_APACHE' writing manifest file 'src/backports.zoneinfo.egg-info/SOURCES.txt' copying src/backports/zoneinfo/__init__.pyi -> build/lib.linux-x86_64-3.10/backports/zoneinfo copying src/backports/zoneinfo/py.typed -> build/lib.linux-x86_64-3.10/backports/zoneinfo running build_ext building 'backports.zoneinfo._czoneinfo' extension creating build/temp.linux-x86_64-3.10 creating build/temp.linux-x86_64-3.10/lib gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -fPIC -I/app/.heroku/python/include/python3.10 -c lib/zoneinfo_module.c -o build/temp.linux-x86_64-3.10/lib/zoneinfo_module.o -std=c99 lib/zoneinfo_module.c: In function ‘zoneinfo_fromutc’: lib/zoneinfo_module.c:600:19: error: ‘_PyLong_One’ undeclared (first use in this function); did you mean ‘_PyLong_New’? 600 | one = _PyLong_One; | ^~~~~~~~~~~ | _PyLong_New lib/zoneinfo_module.c:600:19: note: each undeclared identifier is reported only once for each function it appears in error: command '/usr/bin/gcc' failed with exit code 1 ---------------------------------------- ERROR: Failed building wheel for backports.zoneinfo Failed to build backports.zoneinfo ERROR: Could not build wheels for backports.zoneinfo, which is required to install pyproject.toml-based projects ! Push rejected, failed to compile Python app. ! Push failed  Thanks.

Answer: Avoid installing backports.zoneinfo when using python >= 3.9 Edit your requirements.txt file FROM: backports.zoneinfo==0.2.1  TO: backports.zoneinfo;python_version<"3.9"  OR: backports.zoneinfo==0.2.1;python_version<"3.9"  You can read more about this here and here