@Tamás7 Does your invitee status say that he hasn't signed up or that he hasn't taken a trip yet?
In order for you to receive your Travel Credit for the referral, your friend needs to book and complete a qualifying reservation. In most areas a qualifying reservation is at least $75 USD (or the equivalent in local currency) excluding Airbnb's service fee, guest fees or taxes, if applicable. Your invitation page will state what amount is needed for a qualifying reservation.
Within 2 weeks of the completion of a qualifying reservation, you will receive your Travel Credit.
If your friend used the link in the invitation email you sent to create his new account, he will receive his Travel Credit immediately which will automatically apply to a qualifying reservation.
Hope this helps explain!