id_type "userid" is not documented in the Description of the LookupPatron API.
In the description of LookupPatron API now I see from C4/ILSDI/Services.pm: 273 274 =head2 LookupPatron 275 276 Looks up a patron in the ILS by an identifier, and returns the borrowernumber. 277 278 Parameters: 279 280 - id (Required) 281 an identifier used to look up the patron in Koha 282 - id_type (Optional) 283 the type of the identifier, possible values: 284 - cardnumber 285 - firstname 286 - userid 287 - borrowernumber cardnumber, firstname, userid, borrowernumber are the values from homonym column of borrowers table. http://schema.koha-community.org/tables/borrowers.html