Understanding Temporary Hold Status

The status changes mainly in the following three situations:

1. If PayPal's security model determines that the transaction needs to be reviewed
2. Chargeback
3. When filing an objection

Systematically, 1 is the DoExpressCheckoutPayment call, but 2 and 3 occur at any time after the DoExpressCheckoutPayment call (the buyer's behavior triggers).

If you want to systematically process Temporary Hold in real time (for example, do something when the status is complete), you must be IPN-aware.
(If you change the status on the PayPal side, you will be notified by IPN.)