- Reviewed how POS split payment works end-to-end (modal → sale creation → payment APIs → completion).
- Clarified multi-payment: split across different methods is supported; same method twice was blocked before.
- Enabled 2 lines per method, except cash stays 1 only (Zelle, card, CPP, card reader can be added twice).
- Added clear labels on each line (e.g. Zelle Payment 1, Zelle Payment 2) with amounts and totals in the modal.
- On confirm, Zelle breakdown shows each line and total to collect before staff confirms.
- Database now stores each line with a slot id (e.g. zelle1, zelle2) and a display label for easy identification.
- Terminal payments run one at a time — first CPP/card/reader must finish before the next line is enabled.
- UI shows “Waiting — complete previous payment” on lines not yet their turn.
- Cancel / return-cash modal updated to list each completed payment separately (not one combined total).
- Fixed error “saleId and paymentMethods array are required” when processing saved card lines sequentially (backend validation order).