You can only apply for jobs in a sector you're subscribed to. If a role is outside your subscribed sectors, add that sector in your profile before applying.
Some sectors also require an approved license or certification in certain countries. If a role requires one and you haven't uploaded and had it approved yet, you won't be able to apply until you do - check your profile for what's outstanding.
Your profile also needs to be approved before you can apply for anything at all.