The app keeps every sale on the phone first, and it can’t open that storage. Nothing has been lost, and nothing new can be recorded until this is fixed.
Try this, in order: close any other tab with this app open, turn Private Browsing off, then free up some space on the phone.
Tap your shop, then enter its PIN.
Scan or type the frame number and price. Toggle lenses if they're buying those too.
Cost and suppliers are not on this screen. They come after the customer is served.
What the shop pays for — chai, bijli, transport. Paid now comes off the drawer; pay later stays owed.