Whether you want to spend from one of your Jars or your Wallet, you can also choose a Backup. A Backup is handy for when you don’t have enough money in a Jar that’s linked to your card to cover the whole amount. For example - you are buying something that costs £10, and your card is linked to a Groceries Jar, which has a balance of £5. Choose one of your other Jars as Backup and the remaining £5 will come from there.
To set a Backup, tap the Jar you want as your Backup payment source, tap the Settings cog in the top right corner, then Backup source, and select from the options. If there is no Backup source, tap “Use a backup payment source” to activate the options.