TypeError: CredentialsManager.add() missing 1 required positional argument: 'self'

[addyuchiha]

i am using developmet branch this is the code:

from pyVoIP.VoIP.phone import PhoneStatus, VoIPPhone
from pyVoIP.credentials import CredentialsManager

user = 'fo342155ip301773_00'
port = 5060
pas = 'f045y5wnQs'
servera = 'sip.plusnet.de'

Credentials_manager = CredentialsManager
Credentials_manager.add(username=user,password=pas,server=servera)

if name == "main":
phone=VoIPPhone(server='sip.plusnet.de', port=5060, user='fo342155ip301773_00', credentials_manager=Credentials_manager)
phone.start()
while 1==1:
i = input(">")
if i=='a':
print(phone.get_status())
if i=='s':
phone.stop
break
elif i=='d':
x=input(">>")
phone.call(x)

and this is the error:

Traceback (most recent call last): File "/home/addy/Desktop/x/telephone/pyVoIP/x.py", line 10, in <module> Credentials_manager.add(username=user,password=pas,server=servera) TypeError: CredentialsManager.add() missing 1 required positional argument: 'self'

any help regarding solving it will be helpfull,
thanks