smarty unsupported type: json when inviting people to reservation

[kkrueger61]

[x]: This is a bug and not a question.

[x]: I understand that the best way to resolve this issue is to solve it and propose a Pull Request.

Describe the bug**

I updated from Version 2.8.3 to version 4. Whenever I try to add people to a reservation (invitation or list) the reservation is not updated or saved. The scroll weel scrolls forever I cannot connect to the system and have to wait until something timeouts

To Reproduce**

Steps to reproduce the behavior:

1. Go to a Ressource (use schedule or calender.php ) and try to add a new reservation.
2. Add title, time, date and save.
3. Open the reservation again and add a person to invite, the person appears in the box of the invitations
4. try to update the reservation

Expected behavior**

I expect that the reservation is updated and invitation email is sent to the person BUT the reservation will not update, the box with the scroll wheel and the notice "reservation is updating" is there foreever.

After a very long time (more than 10 minutes) there is somewhere a timeout I can open the startpage again. When I look at the reservation the person who I invited is saved but no email invitation.

Screenshots**

Additional context**

Apache error is: Got error 'PHP message: PHP Notice: escape: unsupported type: json - returning unmodified string in /home/www/doc/15433/dcp154330032/life-bildungsnetz.de/buchungssystem/vendor/smarty/smarty/src/Extension/DefaultExtension.php on line 484;

-> yes in the function smarty_modifier_escape there is no json

Specifications

• LibreBooking version (or SHA if using the develop branch):
  Librebooking Version 4

[kkrueger61]

the error ocurred because of a wrong SMTP port number in the configuration