We worked with four partners to integrate messaging capabilities into their products. People could message their friends about what they were listening to on Spotify or watching on Netflix, share folders on Dropbox, or get receipts from money transfers through the Royal Bank of Canada app. These experiences were publicly discussed and only available when people logged into these services with Facebook. However, they were experimental and have now been shut down for nearly three years. No third party was reading your private messages, or writing messages to your friends without your permission.”]
Source: https://about.fb.com/news/2018/12/facebooks-messaging-partnerships/