Sending data to Backtrace server would naturally require internet connection. But what if the user is offline while getting error? So I tried some error tests while offline. My tests are the following:

• TEST 1 : I test the error while offline, after that I closed the game and turned on my internet. The error data wasn't received
• TEST 2 : I test the error while offline, after that I  turned on my internet.  The error data wasn't received.

Seems like the data only being sent when you get the errors while online. Is there a solution for this?

I mean, gamers aren't always be online unless it's an online game right?  And it's not like we told them to be online if they got error. So, shouldn't there be a way to persevere data until the user is back to online? Like saving them into log files that can be sent to the developer in case they got error while offline or having the game to automatically send the previous error log the next time the gamer opened the game while online or something? Or even better, showing a pop up to send bug report to the developer?

Well, Unity  by default  log every error including ones from Backtrace into player.log, but that's just unity solution