Issues with video format for project delivery

We work with a client who uses GroupShare with Studio 2017. We (their translation agency) are using the Trial Version of 2019, with the Subtitling app (wonderful, by the way!). For their first video project, they sent the SRT file and the corresponding XLIFF. We translated the XLIFF. When we open this project in Studio 2019, the video preview looks perfectly well, with the target language subtitles. When we send the project back to them via Groupshare, however, they open the video on their end, no subtitles. When I opened the target project folder, there is only an MP4 video and the target XLIFF, not an SRT file. Is there anything that either the client or we are missing?