It is not really matter. But why don't you make it a paid plan? You can enable offline payment plugin so that users do not have to pay at the time they sign up, and you can send them the payment link later ?
I assume that the user will have to log in to the account to pay later. This would not be possible as the person paying is different from the end user so they won’t have the login details
You can use Request Payment feature to send payment link to them. They can send that payment link to the person they want so that the person can process payment (without request to login)
