Dial-in in Webconference. PIN not available

[SEG]

I have configured Dial-in in the conference section with a dedicated DID.
It is possible to Dial-in, but then the user is asked for a Conference-ID.
There the problem starts. According the following howto, the Conference-ID is visible on the "add participant" window.
https://www.3cx.com/blog/releases/dial-in-web-meeting/

But the add participant window does not show this information. Also the window does not allow to add a dial-in user.
Therefore the user gets the invitation email from the template: "Conference Audio - and Video" and not from the template "Conference - Audio only"

For testing I added the following attribute block to the "Conference Audio and Video" template. But it seems that this attributes have no values. It sends empty values in the email I get. Excepted the extension information. "Dial 700 and then PIN (missing)

<p>
Joining info:<br>
%%IF_EXTERNALNUMBER_PRESENT_START%%
Dial %%EXTERNALNUMBER%% <br>
Enter PIN %%CONFERENCEID%%.<br>
%%IF_EXTERNALNUMBER_PRESENT_END%%
Internal employees can join by dialing %%INTERNALNUMBER%% and enter PIN %%CONFERENCEID%%.<br>
%%IF_MEETING_NOTES_START%%
Notes: %%CONFERENCEDESC%%
%%IF_MEETING_NOTES_END%%
</p>


Any ideas appreciated.

Version: 16.0.1581 Professional.