If you make changes, for example on your products, store, or account, you need to do a refresh on the app. You can do this under Settings > Account. There are 3 types of refresh: 

Refresh Products - for all product, tax, category, and catalog order changes
Refresh Account - for account level changes, such as employee PIN, going live, changing your customised receipt
Refresh Transactions - For transactions that are only stored on your device and need to be synchronised to the server