Staying abreast of your financial transactions helps you to keep the right balance in your account. PayPal has backup funding sources that help ensure you never fail to pay a charge simply because your PayPal account itself is low. Knowing when the charge will go through can help you to plan your finances accordingly.
You choose your own backup funding source from the accounts linked to your PayPal account. You can change it whenever you need to do so, switching between various connected bank accounts. If you use the PayPal debit card, the backup funding source also covers charges made on that card that can't be covered by the funds in your PayPal account.
When PayPal attempts to process a transaction and isn't able to, it tries to use your backup funding source right away. There is no delay. PayPal completes the transaction quickly, immediately removing the funds from your backup source and paying the charge.
If a transaction is processed by PayPal and you weren't expecting it, you may not have sufficient funds in your backup account. Once PayPal attempts to use backup funding and isn't able to, the charge will be declined or PayPal will overdraft, depending on the type of account. When funds are next deposited into your PayPal account, they will be used to correct the overdraft.
Choosing a Source
When choosing a source for backup funding, pick one that has sufficient funds to cover unexpected charges. An account that holds extra money for savings, for example, may be able to cover a charge you weren't expecting and save you from overdraft fees. You can change your backup funding source directly from your PayPal account.