Very long busy tone after hangup of call from intercom/door opener

I have an intercom/door opener connected to FreePBX via a grandstream HT704.
Asterisk Version: 11.23.0

When pushing the button on the intercom a ring group is activated.
When I answer the intercom call on one of the phones in the ring group and then hangup that call on that phone the intercom will generate a busy tone for almost a minute.
Is there a way to end the call on the intercom without the busy tone or to shorten the time of the busy tone?

There might be a setting on HT704 for this congestion/busy tone period

I tried to find one but found nothing.