Bug Warning: If you accidentally enter a mega raid lobby with a paid pass, and immediately back out before it starts and re-enter with link charges, it will still use your paid pass instead.
When you re-enter, it will look like you're entering with the link charges, but when the raid completes the link charges won't have been used but your paid pass will be consumed.
Support is also unwilling to do anything in this case.
The first time me and my friends saw this, we were pretty sure, but weren't absolutely certain. This time, I immediately was like 'oh shit' as soon as I accidentally tapped in using the raid pass and then after noting my link charge amount I carefully and consciously selected my link charges when re-entering and the glitch happened again.
To work around this, me and my friends before mega raids have taken to all verbally confirming to each other that we're toggled to link charges before anyone clicks into the raid.
Once you've entered once, I'm not sure if there's anything that can be done to save that raid other than not doing it. I wonder if waiting for the existing lobby to expire or waiting long enough might reset the pass, but it's not exactly something I'm eager to test on purpose.