My flask application is always crashing. When I start the application it is successfully built, and there is no issue found in build logs in it, but when it start deploying it crashes immediately showing this message : /bin/bash: line 1: gunicorn: command not found, and 502 bad gateway when i click on the link of the application.

I am using JSON to configure the application.

{

"$schema": "https://railway.app/railway.schema.json",

"build": {

"builder": "NIXPACKS"

},

"deploy": {

"startCommand": "gunicorn main:app",

"restartPolicyType": "ON_FAILURE",

"restartPolicyMaxRetries": 10

}

}

my requirements.txt are :

blinker==1.9.0

click==8.3.0

colorama==0.4.6

contourpy==1.3.3

cycler==0.12.1

filelock==3.20.0

Flask==3.1.2

fonttools==4.60.1

fsspec==2025.9.0

imageio==2.37.0

itsdangerous==2.2.0

Jinja2==3.1.6

kiwisolver==1.4.9

lazy_loader==0.4

MarkupSafe==3.0.3

matplotlib==3.10.7

mpmath==1.3.0

networkx==3.5

numpy==2.2.6

opencv-python==4.12.0.88

packaging==25.0

pillow==12.0.0

psutil==7.1.0

pyparsing==3.2.5

python-dateutil==2.9.0.post0

scikit-image==0.25.2

scipy==1.16.2

six==1.17.0

sympy==1.14.0

tifffile==2025.10.16

torch==2.9.0

torchvision==0.24.0

typing_extensions==4.15.0

Werkzeug==3.1.3