Indexed repeat error in app

Dear Community,
Please help with this indexed repeat error message above. the form is well validated on the web form but once I use the phone app it brings an error like this in the photo. I have repeat group within a repeat group and at the end of the survey, i want a total of each entry in this repeat group. The other calculations out of this group are working but this one has failed. I have attached images showing part of the xls form. I have read through different submissions but I do not clearly understand what i should do. Thank you.

@Maria4, have you validated your XLSForm through this online validator to see if there are any syntax issues?