Im not going to be any help on the specifics, but consider what features are wanted/needed.
If it’s effectively an electronic copy of a business card with some details and a QR code link to a web page / social media etc then a full on service with a subscription isn’t needed
But if they want the QR code link to go to x today, but to Y next week when running a particular promotion and to Z in a month then a subscription service fits the bill
Most of the ‘free’ generators require an account which can be free, but added features cost on subscription
The generated QR code never points to your business but to the host and they redirect to a selected location
If you end the subscription then every copy becomes worthless and doesn’t redirect
At least if it pointed to one website or social media you could leave a redirect if you go to another media
Some QR generators will go to the address you choose
To test that create a QR, wave a smart phone camera over it and see what the link shows.
If it says www.mybusinessname.com then that’s where it will always go
If it says www.hosting.com/redirect1234567890 then it goes to the host and bounces to the selected address. That allows you to manage and keep changing, therefore old copies will go to your latest choice ….. until you stop subscribing
Once you have a QR don’t just leave it on the digital card. Save the image and embed it everywhere
You can also create QRs for everything, website, Facebook, linkdn ……
Then embed the QR image onto a Facebook logo (or a ‘find us on Facebook logo’), linkdn logo etc
You can recolour a basic black & white QR into themed colours, such as your friends branding, Facebook blue etc