Hi Florian,
Thanks for your response. I am sure the problems I was having were not generated by your procedure. It appears that the sync client on the Raspberry Pi must be set up locally but can subsequently be used headless (I am using XRDP and rdesktop. I have multiple RPis serving multiple purposes and an Acer Atom laptop to run all headless via ssh or XRDP as the occasion requires.

As a matter of interest I think a lot of the problem was caused by
1. Data quantity (I have now preloaded the second RPi using rsync from the original source)
2. Low power (using a ‘bigger’ power supply on the Nextcloud server)
3. Temperature (I’m in Australia and we are coming into winter but the ambient temperature is sitting between 18 and 24 C – during the failed attempts on the large data set the RPi temperature got to 79C – in summer the RPis regularly get to 60C at idle – I’m working on getting fan cooling before next summer).

Thanks again for your tutorial.