a server internal error at JoinCallAsync

This is a question about the PSIBot sample.
I have been trying to make the bot join a scheduled meeting by entering a joinWebUrl in the management page, but so far it's failed with a server internal error at JoinCallAsync (which is defined in \PsiBot.Service\Bot\BotService.cs):

[...]

The HTTP status code of the response was 500.

The joinWebUrl that I am using for the trial is:

https://teams.microsoft.com/l/meetup-join/19%3ameeting_Y2QzZDg1NTUtNjFhMy00OGMxLWEyMGQtMDE5YmYxNDVmN2Yz%40thread.v2/0?context=%7b%22Tid%22%3a%22{{tid goes here}}%22%2c%22Oid%22%3a%22{{oid goes here}}%22%7d

Since the url somehow looks different from what the original ParseJoinURL function expects, I changed the regex rule a little as follows:

I inserted Console.WriteLine("[Debug NNN] ...") lines in the code so that you can see that the objects are successfully extracted. Accrding to the output by the lines, the parser looks successfully extracting the objects before the JoinCallAsync function was called.

Please advice if you have any idea what could be the problem and how to fix it ?
I appreciate your help in advance.

Start in PsiBot.Service/Bot/BotService.cs and trace ParseJoinURL into JoinCallAsync using the supplied joinWebUrl and the reported HTTP 500 response. Compare the URL format and extracted values with the existing sample behavior; done means the bot can join the scheduled meeting without the internal error.