Discount for someone using refer and earn link doesn't work for some plans

When my friend wanted to buy a 5GB monthly plan with the 50% discount using my refer and earn link, the discounted price doesn't show up at all - even at the point when they're just about to purchase. Seems to be the same problem if they try to buy the 50GB plan and one of the unlimited plans. Same thing happens if they use someone else's refer and earn link. No problem when trying to buy other plans.
They do deactivate ad blockers and have enabled cookies.
They used online chat and called Lebara - both times simply told to delete browsing history and try again - which doesn't work. Anyone else encountered this problem?

Hey Al2026 I can get someone to look into whats happening with the referral link. I'll send you a direct message to take some details.