There are a lot of online sites where you can create scannable tickets, but often it is “freemium”. Meaning there are features that are free and there are other features that will cost money.
Here are some sites:
To make a scannable ticket yourself and manage it would require some knowledge of coding.
A low-tech way is to generate numbers and use an Excel sheet, then have someone (like a bouncer) check the ticket number code. A word of advice don’t use 001, 002, 003, etc. Like a strong password, use a combination of numbers and letters. That way it’s harder to counterfeit.