I solved it as follows
- I copied the ifcfg-eth0: 1 file and renamed it to ifcfg-eth0: 2
- I changed the ifcfg-eth0: 1 file with the IP where the Plesk license is
- I put the IP failover in the file ifcfg-eth0: 2
- Then at Plesk I asked to reread the IPs
For now it is resolved, I believe that...