As you remember from our previous lessons, verbs with an inseparable prefix such as be-, er-, ver-, zer- do not put ge- in front. This applies to regular verbs such as bezahlen and verkaufen and also to irregular verbs such as verlieren:

Er hat das Essen bezahlt. – He’s paid for the meal.
Wir haben das Auto verkauft. – We’ve sold the car.
Ich habe meinen Terminkalender verloren. – I’ve lost my diary.