Why is the PPSN Number a requirement to pay LPT?

I'm trying to pay the property tax for my mother in law who is in her late 80's. I logged in and I find that I cannot use the details provided on the letter without her PPSN, which no doubt she has no idea about.

I spoke to the helpline who confirmed it is necessary; but could not explain why, other than it is required. They did tell me where to find it though.

I now need to make her aware that I'm paying it which will worry her, as she will want to pay it back when she can't afford to.

Why when I have the property ID and pin and I'm happy to pay on her behalf do I need a PPSN?

its required as one of the penalties for non-compliance is a surcharge on your income tax (if you are self-assessed).

Thanks Nige - this person will be compliant pensioner if I could pay it for them so I still don't get it.

Has your mother-in-law a medical card, a pension payment card or any documentation issued by Revenue, HSE or Social Protection / Social Welfare? They should show PPSN.