List Payment Groups

Lists all payment groups with filtering, sorting, and pagination (including JSON path filters on metadata, e.g. ?metadata[externalKey]=...). Pass withStats (e.g. true, yes, bare ?withStats, or withStats=) to enrich each row with paymentCount, totalAmount, and totalAmountRemaining (when member refunds apply) aggregated across member payments (single member query, regardless of page size). Combine with include=invoice to also load the assigned invoice — both are how the PaymentGroupsTable and its row dropdown (assign when OPEN; sync eligible Mollie payments; delete when OPEN with no payments) consume this endpoint.