skinparam monochrome true
participant "SEQR App" as SEQRApp
SEQR-->Merchant: (unique reference)
SEQRApp->SEQR: ask for invoice at point of sale or using reference
Note right of SEQR: retry until you get SUCCESS
SEQRApp->SEQR: payment (with uniqe reference)
Note right of Merchant: Payment cleared!
SEQR->SEQRApp: Done (show receipt)
Create a bill and publish it to the app
You will need PIL and qrpython library (pip install qrcode PIL suds)
The point of sale must check the status each second, to verify that payment is completed. Otherwise the SEQR server does not receive any notification that transaction is finalized and the purchase will then be reversed!