vedholdenhed

13:16 Apr 25, 2018 

:)

12:59 Apr 25, 2018 

This is one of those cases where you wonder if the writer has understood what a word means, in this case perseverance, as you say (presuming that perserverance is a typo).

Perhaps they meant retention.

I would ask the client. If no reply is received before the deadline, I would translate what it actually means, perseverance, and add a note that it is quite possible they really meant retention.