Error in using a function "climdexGrid()"

[xiaoyujiaxyj]

Hello!
According to the definition of the climate index "Rnnmm", nn is a user defined threshold. When I tried to calculate the "R1mm" by using "climdexGrid()", it told me error in match.arg(index.code...). How can I define the nn threshold?
The code is:

R1mm <- climdexGrid(pr = prdata, index.code = "R1mm")
Error in match.arg(index.code, choices = c("FD", "SU", "ID", "TR", "GSL", :
'arg' should be one of “FD”, “SU”, “ID”, “TR”, “GSL”, “TXx”, “TNx”, “TXn”, “TNn”, “TN10p”, “TX10p”, “TN90p”, “TX90p”, “WSDI”, “CSDI”, “DTR”, “Rx1day”, “Rx5day”, “SDII”, “R10mm”, “R20mm”, “Rnnmm”, “CDD”, “CWD”, “R95pTOT”, “R99pTOT”, “PRCPTOT”

Thank you in advance!