Issued invoice including invoice line items and price list details:
https://demo.flexibee.eu/c/demo/faktura-vydana.xml?detail=full&relations=polozkyDokladu&includes=faktura-vydana/polozkyDokladu/faktura-vydana-polozka/cenik/
Payment ID of a proforma invoice via relationships:
faktura-vydana/(typDokl='code:ZÁLOHA'%20and%20stavUhrK%20in%20('stavUhr.uhrazeno','stavUhr.uhrazenoRucne')%20and%20id>=10).xml?detail=custom:id,varSym,datUhr,vazby(typVazbyK,b(id),a(id))&relations=vazby&limit=0&includes=/faktura-vydana/vazby/vazba/b/