Tested on PixivPy 3.7.0:
_ACCESS_TOKEN = ""
_REFRESH_TOKEN = ""
from pixivpy3 import *
api = AppPixivAPI()
api.set_auth(access_token = _ACCESS_TOKEN,refresh_token=_REFRESH_TOKEN)
res = api.novel_text(21269184)
print(res) #{'error': {'user_message': "Specified end-point doesn't exist", 'message': '', 'reason': '', 'user_message_details': {}}}
This method has been affected since the latest update of Pixiv APP.