Trouble generating valid SRT captions file for Vimeo or YouTube

I created captions within FCPX. Everything went smoothly and then when I exported the video I had it create a separate .SRT file. That file apparently doesn't work for Vimeo or YouTube even though they claimed it would. Vimeo ignores it and YouTube says there are errors on 2 lines (end of explanation). Is anyone doing this successfully that can give me a hint what I'm missing here? Thanks in advance.

YouTube probably is right - from their point of view.
You could try a freeware like Jubler to verify your SRT.
One important thing: any special special character like @ or note signs will/can cause trouble.

Thanks for the suggestion. My biggest frustration is that Apple has this very cool process to create captions and then the outputted file doesn't work on either of the top 2 video streaming services. Is this a bug? I'm going the 3rd party captioning solution for now (with deadlines & such to deal with) but I'd definitely like to know if FCPX's captioning functionality works or not. I don't think going into the code of the captions file should be necessary.

Even though there are lot of "not so perfect things" using captions/subtitles with FCP I'd say Apple for these things is the the most reliable.
YouTube and Vimeo are very picky to have a very simplified file (Netflix very restrictive in other concerns) - so it's probably not an FCP error. But it might be an user error not be informed enough about restrictions, rules etc
Try to export SRT without formatting (YouTube and Vimeo don't like it - Facebook, etc either). Double check with another app.
For YouTube you might try an scc file.

Okay, I finally figured it out. For me the key was exporting the SRT file with it being both unformatted and exact timing. That seems to give the file format that Vimeo & YouTube like. Hope that helps someone else down the road.

The main thing really is to have NO formatting applied to the SRT.

Another thing I do now so one SRT works across Youtube and Facebook and Vimeo is to add a country code to the filename. eg. 'Master-Annabelle.en_GB.srt' where en_GB stands for English UK.
Country codes list here: www.facebook.com/help/1528795707381162?helpref=faq_content