Military Times (the second paragraph is quoting the complaint, I think):
Voxer launched the app in 2011, which was named Best Overall App in the First Annual Silicon Valley Business App Awards in 2013. In 2012, Facebook approached Voxer about a potential collaboration that led to Voxer sharing its patents and proprietary information with the company.
“When early meetings did not result in an agreement, Facebook identified Voxer as a competitor although Facebook had no live video or voice product at the time,” court filings read. “Facebook revoked Voxer’s access to key components of the Facebook platform and launched Facebook Live in 2015 followed by Instagram Live in 2016. Both products incorporate Voxer’s technologies and infringe its patents.”
The Verge from 2013:
On its developer blog, Facebook's [representative] responded, although very indirectly, to removing access to new video app Vine's friend-friending ability yesterday just hours after the app launched.
Evidently, sharing back isn't always enough. Vine doesn't, after all, send the video clips you make to Facebook — it only sends a link to your video, effectively moving your engagement offsite. Facebook's objection is in that regard understandable, though when combined with several other similar clashes lately with app developers like Voxer and Yandex's Wonder, Facebook sounds like a bully.