You will be needing:
2 installations of path of exile, one from steam and another one from the website.
Process Explorer https://learn.microsoft.com/en-us/sysin ... s-explorer
Steps:
1 - Open one of the path of exile.
2 - Open process explorer, select the current path of exile process.
3 - CTRL + L in process explorer, with path of exile process selected.
4 - Kill handle Mutant \BaseNamedObjects\PoERunMutexA
5 - Now you can open the other path of exile install
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*be aware, this is not a intendeed game behaviour. Maybe can lead to account ban?