Creating a random string to be used as an order/invoice ID (or anything else for that matter) is something that can be done pretty easily. Here's
Pick a Formatter step and choose Numbers -- Spreadsheet-Style Formula. Then use RANDBETWEEN:
The odds of ever having a duplicate are extremely low. If you wanted to, you could create two of these steps then combine the mapped fields, to make it even more unique, but there's probably no need.
You could also create a Pick From List, choose random and have some preset options to choose from that you can add to the randomly generated number.
OR, yet another way is to either use a field from the Trigger (or prior step) on its own, or combined with the randomly generated string:
Hope this gives you some inspiration for how to randomly generate a string! Are any of y'all generating or using random strings within your Zap and if so, how are you using them? We'd love to hear about your use cases!