From kalilinuxtutorials.com
On-The-Fly was written in Python and made extensive use of Scapy and netfilterqueue. It is crucial to have Scapy in Python and net filter queue installed with a compatible version of Python. For this, a version of Python 3 up to Python version 3.7.5 is recommended (and no higher, as there may be incompatibilities with 3.8 and 3.9 in some libraries that it uses ‘on-the-fly’). There is a requirements.txt file that must be executed the first time the tool is launched using ‘pip install -r requirements.txt’. Again the pip version must be oriented to a Python 3 version up to 3.7.5.