1)Customers data you can find on Telinta -> customers-> webself care tab and here you will find two fileds passworkd and email address these are to be synchronized. Please note that pass on that field you can choose any cahracters evet like test 123 and it will accept it which means there is not encrypted mandatories set for that.
2) this could be found in the customers list did you checked Telinta customers page?
3) the customers login should be the same email as from 1) otherwise it wont work all API root data is very sensitive library data and we need to set it right at the very beginning before we come to more complex works such us orders managements and orders payment later on.
From VoIP Customers Authintification job you should alrady know by now that customer login email is the one which in Web self care same for pass if the pass changed there by Telinta admin then customet can login to voip using the same pass set on Telinta webselfcare. WOtherwsie we wone be able to complete an order for the customer when ones orders numbers and pay (in later jobs)