A medical certificate is mandatory by the organizer. Italy legally requires that people participating in sports events must provide a medical certificate. This is not a COVID-19 related certificate and pre-dates COVID-19.
In order to participate in the camp, you need to provide a statement from your doctor that you are physically and mentally healthy to participate in BJJ training.
You should ask your doctor to provide you with the document (see examples) or the organizer can arrange a medical exam on the spot that will cost 35€.
No people will be allowed to train without this document!