Server lags and kicks host

Actually you are not even the host, so that has nothing to do with it xD

Basically, what the text down below is saying is that there is not rly much you can do when it comes to modpacks.. Since they are pretty heavy, and you cant remove a separate mod in a modpack.

Our standard mod/modpack reply:

If you are using mods, and the server wont start, then it is most likely a broken mod, or maybe one of your mods need a support mod. So, to fix a modded server not starting, check you logs if there is a broken mod, then just delete that particular mod. However, if you are using a modpack, there is not much you can do, since you can not delete a separate mod in the modpack.

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A mod/modpack might run just fine when you started to use it. But it can break at any time. Some might not even start. Cause the more you use it, the more RAM you need, and since aternos has a RAM limit (Cant rly complain, its free) it will eventually give up and start to crash.
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We always try to get the best possible balance between our limited resources (since we are free and we don't want to change that) and the best performance. Especially for modpacks, this is really hard to achieve. We test the modpacks in our system to ensure that they are at least starting and that basic playing is possible. Because modpacks are always a bit different and the load on our host systems is also always different we cannot guarantee anything here. But we decided to still offer modpacks on our platform because we want to offer as many options to customise your server as possible and most of the modpacks are pretty playable most of the time.

Btw, if there would be some sort of fix, you should find it in your logs

You cant install plugins when using mods