NoDMarkerAndNotEmpty problem - privileges not the problem

Hello dudes i was setting up a testnet for the cardano node because i am in a learning phase but i got stuck when i wanted to run it… I have this problem:

NoDMarkerAndNotEmpty "home/xxx/cardano-src/testbet/db/protocolMagicId
cardano-node: Missing “home/xxx/cardano-src/testnet/db/protocolMagicId” but the folder was not empty…

Is this protocolMagicId some file or something? I do not understand… Saw other post and the privileges were the problem… In my case i checked them and also re announced them but the problem persists…

I downloaded the required files from here: Environments - The Cardano Operations Book

Also i try to run the node with this command:

cardano-node run
–topology topology.json
–database-path db
–socket-path db/node.socket
–host-addr “my public ip”
–port 3001
–config config.json

Can you help me please?