Regarding API openness vs flat file.. we in the OMS space have our hands tied by the WMS, ERP and EDI world. Investment in an open API doesn't really have any ROI it's actually more of a money pit than anything. Most of the high value integrations are with antiquated systems where all of the connectivity is flat file CSV, XML, EDI type thing. It's awful.
There's also very very slim margins the shipping / fulfillment middleware market. It's incredibly costly to maintain these legacy proprietary connections, mission critical to the business so near constant customer service requests with complex "we're on fire" troubleshooting, and nobody wants another expense lumped onto their shipping costs so it's very hard to justify paying a premium.
Not surprised that any company in this space backed by VC is getting dumped by their investors like a hot pile of bricks. OMS is about consultation and pain endurance, not venture exits