I want to send bulk SMS on WhatsApp without creating broadcast list.
For that reason, I found pywhatsapp package in python but it requires WhatsApp client registration through yowsup-cli.
So I've run yowsup-cli registration -r sms -C 00 -p 000000000000 which resulted in the error below:

INFO:yowsup.common.http.warequest:{"status":"fail","reason":"old_version"}
status: fail reason: old_version

What did I do wrong and how can I resolve this?
The problem is with the http headers that are sent to whatsapp servers, these are found in env/env.py
The name of headers are manually provided, therefore due to new updates whatsapp servers only serve or authenticate to updated devices which is identified with their http/https/etc headers, in this case you need to update some constants in the above file(env/env.py) in your yowsup folder.
How to send bulk sms on whatsapp