I work as a physiotherapist. Can I join the Edenred merchant network?

Yes you can, if your services include massage services too, as the massage benefit can be used only for massage services.

According to the Finnish Tax Administration the massage benefit cannot be used to pay for physiotherapy services.

Physiotherapy is not a massage, as it usually aims to cure or prevent an injury. Physiotherapy organized by the employer therefore is not tax-deductible recreational or hobby activity. (Translated from Finnish from the Tax Administration's website (3.2.5.5.).