Error at checkout "Unsupported operand types: int + string"

Error at checkout "Unsupported operand types: int + string"

Hello,
on the final step of the checkot precoess when I click the order button, I get the following error message:

Unsupported operand types: int + string

I'm running PHP 8.0, when I switch to 7.4 it works fine. Is there any fix to this?
Thanks!

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Aw: Error at checkout "Unsupported operand types: int + string"

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