Solved it partially (mea culpa -> RTFM! wink )

NFA=0 (NFA Flag must not be set)
Hedge=0 (no hedging)
Hedge=4 or 5 (virtual hedging, ZorroS required)

But the question concerning the lot size remains.
My understanding is that Zorro synchronizes lot sizes via the API. When restarting Zorro the resumed positions are listed, but the lot size displayed is not the one I see in my Oanda account:

Zorro:
[USD/CAD:HP:S00192] - resumed (843 lots)

Oanda:
ID 186 USD/CAD 465 Short

My plan is just to wait until Zorro tries to close the trades with an error message and than closing the trade manually on the broker platform.

Is there no other way to synchronize the open trades between Zorro and the broker via the API?

Cheers
Michael