Anyone may pay another resident's tier as long as they know where the tierbox is. You would simply right-click on the tierbox, select Pay, and then select the number of weeks. Once the payment is made it's important to wait until you receive the dialog box that asks if you wish to credit their lease. Simply click "Yes" and the payment will be correctly applied.
Where is their tierbox?
Due to privacy concerns we do not divulge the location of someone's tierbox. We also do not provide the time remaining or the cost per week they are currently paying. This is to protect the resident in the event someone is attempting to gain information that should not have it. However, you can still pay on their lease provided you can provide certain information.
In order to credit someone's lease without knowing where their tierbox is we do allow one-time payments to the kiosk in our land store. You would pay the standard Dream Seeker Estate rate for the parcel type and size (which can be provided by our staff) and provide the name of the tenant you want credited. If possible it would also be best to provide the SLURL of the parcel/region you want credited. This payment would then be applied based on the cost per week of the parcel/region.
In the end it is always best to get the tierbox location from the tenant so that you can pay directly on their lease. This would allow you to keep track of how many days are remaining, how much the lease is per week, and avoid the extra steps of paying on their lease.