How to automatically route outgoing calls to bluetooth head set

[Dubonnet]

I make calls through a dial up tool on my laptop.

Laptop sends number to S9 over Bluetooth.

My PLT headset is well connected with the S9.

But when calling, the audio is on phone speaker and not routed to the connected bluetooth headset.

Never had this problem with other phones.

Where is the setting to automatically select headset when calling?

Thanks for your ideas.

[Ian29]

Hi there, my 

I am expirience the same issue on my Samsung S10+,  android 10.

The call audio is not routed to the bt device when making an outgoing call. 

However, the call audio is routed correctly when receiving and incoming call. 

Thanks in advance.