I think you are talking about the “Specified visa: Designated activities (Long Stay for sightseeing and recreation)”.
As you can tell by the Ministry Of Foreign Affairs website this is basically an extended tourist visa and is meant for tourism and sightseeing. What you are allowed to do is similar to a tourist visa though. Paying for recreational acitivites is however a basic for of a vacation or sightseeing. However, being payed to do something is not really covered under the guise of sightseeing and recreation
Perhaps more easily understood as colloquial English, and as @pnuts notes, written another way and with the same meaning: you may not engage in activities for which you are/will be paid.
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