Welcome to the community, Xeaghoinno53!
A flashing blue light on the Connect Box 3 Fibre indicates that the modem is currently attempting to register with the Sunrise network. This status often relates to a missing WAN IP or a potential cable issue, which is why a check of the fiber optic cable and the OTO port configuration can be helpful. More details can be found under Connect Box 3 Fibre - Technical details and explanation of… . Keep in mind that fiber optic cables are highly sensitive to being pinched or bent too sharply. However, if the cabling is correct and in order, the cause can also be a provisioning error on the line. If the connection fails to establish within 30 minutes, it is best to contact the hotline (0800 707 707).
Cheerio, cosmo