When creating a direct entry payment file, or processing super you may be prompted for a User ID, which usually resides under Company >> Bank Account >> User ID.
This is always a six digit number.
For most major banks (ANZ, Westpac, NAB) it is six zeroes (000000). For CBA it is 301500. For any other financial institution you will need to contact them and ask for the Direct entry User ID, or APCA ID.