Developers installing Certbot on Raspbian 11 (Bullseye) with Python 3.9 often hit build failures. The core issue is dependency compatibility on ARMv7l architecture. A reliable workaround involves pinning the cffi package to a version below 2.0.0, ensuring pip resolves a known-good combination without compilation errors.

This approach provides a stable path for constrained environments. The alternative requires installing the system's libffi-dev package to build newer cffi versions. Both methods avoid changing the OS or Python version, offering practical solutions for maintaining SSL certificates on Raspberry Pi devices.

The community-tested strategy highlights a common challenge with Python packages on ARM. Pinning dependencies is a standard practice for ensuring reproducible builds. For Raspberry Pi users, this workaround enables continued use of Certbot without resorting to complex system modifications or alternative ACME clients.