I had tried umpteen time to backfill with Nest 3.13 and RTD 1.5 it wouldn't, although I was able to get quotes to Ami with the same configuration. When I asked the broker to look into it, they said certain files were missing and replaced those files in Nest plugins folder (Omnesys>NEST3>NEST Plugins). After that I got the backfill going. Later I tried another brokers Nest 3.13 and didn't face any such issues. So brokers tweak Nest.