Can someone else pay into my ISA?

No, someone else can't pay into your ISA - at least not directly. 

The ISA rules, set by HMRC, say that contributions to an ISA must be made with your own cash. You can add cash to your own ISA using a debit card or transfer from a bank account in your name - or a joint account you own.

This means that someone else can’t directly add cash to your ISA.

The exception to this rule is a Junior ISA which can accept cash from anyone. Provided there is enough Junior ISA allowance remaining.

What if I need to pay into someone else’s ISA?

If you are looking to pay cash into someone else’s ISA, you can send them the cash first to their bank account, and they can then make the contribution using an instant bank payment or their debit card.