Backup Payment Method not working

[LoboLives]

I'm finding that when I send money Paypal advises "if you don't have enough funds on your first payment method we will use XXXXX card as a backup" but this isn't actually happening. Transactions are going through on the first method but when the money is actually taken out it doesn't switch to the backup payment method if there's not enough funds. 

For example if I send $100, the funds aren't withdrawn right away. So if by chance I have less than $100 in my primary method before the transaction is actually processed all this does is send me into overdraft instead of using my backup method to cover the difference. 

Is there a setting I'm missing? 

[kernowlass]

@LoboLives 

Paypal don't know whether there are enough funds in your first method funding source so have to debit that first.

If the transfer fails then they may put your account into negative and then try your back up funding source.