I'm trying to book a DONE6 ex-TYO and running into some trouble with the online tool.

Itinerary is:

NRT-CMB-SIN-SYD-sAKL-SCL-EZE-GIG-sLPB-MIA-SFO-xLHR-FCO-xDOH-JNB-xHKG-NRT

Attempting to price this with the online tool gives me the fun error: "We have encountered a problem pricing your itinerary. Please save your itinerary then contact Sri Lankan Airlines to book it. [Error: cca34435e76788c]". (NRT-CMB is on UL).

Some questions:

1) Does anyone see issues with this routing?
2) Assuming it is in fact valid, how hard will it be to book this with UL? (I am US-based.)
3) In a couple cases (AKL-SCL and SFO-FCO), there are direct flights that show D availability on EF, but the tool does not always bring these flights up. Is there some other criteria beyond D availability required to book flights on a DONEx?

Thanks!