You can define an ID under the passwords fields, then setup the pass-in fields under pass-in fields. Then set the maximum number of respondents for that ID. If you want the ID to be used once only, set Max Respondents to 1, otherwise set it to your desired limit.
You can create as many unique IDs as necessary. They may have the same pass-in fields as other IDs. No issues there.
You cannot have the same ID multiple times with the same or different pass-in fields. You will have a warning displayed to correct it.
Imagine you was using ID=12345 and it contained 2 pass-in fields as follows ...
Age
Name
Let's say you were allowed to define the ID twice.
ID=12345, Age=22, Name=Max
ID=12345, Age=47, Name=Samantha
If you were to send a survey link to a respondent where ID=12345 was included, how would you determine if they received the "Max" or the "Samantha" pass-in fields? By using different IDs will allow you to have this working correctly.
