Why are most Bitcoin payment invoices time limited ? Most bitcoin payment gateways issue time-limited payment invoices. Why is that ? AFAIK, the address stays valid even after the timer is out. For instance when sending a transaction from wallet to wallet, even if I send to that address after the 15 minutes, the recipient still gets their money. I have tried this with at least 3 wallets. In this case, what's the timer for in the first place if the address is still linked to that user ? 

Thanks.
Most invoices are timed to ensure the price of bitcoin (or any crypto asset) does not move too much.

Although Bitcoin is usable as a currency, it's current volatility is somewhat undesirable. Timed invoices are used to ensure that merchants get a roughly expected $ value.