You are not the only one confused about this term “add on credit card”, this is the same as the name suggesting “an add on” or “supplementary” card.
An add-on credit card is nothing but a copy of your main (primary) credit card, which you can give to your family members, usually your parents, spouse, children (above 18 years), or siblings. It’s linked to your main credit card account and shares the same credit limit.
Still wondering what is add on credit card, let me give you a scenario, suppose you have a credit card with a ₹1,00,000 limit. You can request the bank to issue an add-on card for your wife. She’ll get her own card with her name on it but all the spending she does will be deducted from your ₹1,00,000 limit. You’ll get one combined bill for both cards.
So, yes in add on credit cards the main credit cardholder is responsible for all the payments, even the ones done through the add-on card.