If you are planning on importing payments on to recurring gift schedules then you may want to map a reference code to be stored on the gift. The payment process attempts to find a corresponding RG template record. It does this by a number of methods.
1. The first record that it finds (this is ideal when you are sure that there is only one RG template on a constituent)
2. By matching on the reference field
3. By matching on the reference number field
4. By matching on a gift attribute. This should be a text or number attribute. (Recommended)
The identifier should be unique to that recurrence. For example, if I decide to pay $10 each month then the RG Schedule should contain a unique ID that should also be present in each RG payments too.
What do you do if you do not have a unique recurring ID but may have more than one RG Schedule on the constituent's record?
You may want to use the constituent ID (or an other ID specific to the constituent) instead. You just need to make sure that if you terminate an older RG template record that you also remove the constituent ID from their reference field.