Fundraise Up creates Customers in your Stripe account when processing all one-time Donations and the first Donation installments of Recurring Plans.
As your Fundraise Up account processes any donation through Stripe, it will create Customers in your Stripe account for each new one-time Donation and each first Donation installment of a Recurring Plan. Those Customers are used so that subsequent Donation installments, or attempts to retry transactions, can be run against the payment method saved on those Customers in Stripe.
Customer matching is not performed as that can adversely affect processing and introduce errors. So, if a donor returns and makes another one-time Donation, in Stripe we'll still generate a new Customer for that new Donation.
We strongly recommend not making edits directly in Stripe to any Customer or payment method saved on that Customer used by Fundraise Up. If such changes are made, we cannot guarantee backwards synchronization of that data and it may break the recurring charging of their plan.