I haven't tested webhooks with Telegram, but I think the issue is with how JSON is parsed and the log message.
JSON consists of value pairs with "<field>":"<value>" (like "chat_id"="5").
The log message is 'date=2022-05-04 time=09:42:28 logid="0100032001" [...]' <- there are quotation marks starting with logid.
I think the Telegram API treats that 'logid="' as end of the value for 'text', because of the quotation mark. The quotation marks would probably have to be escaped:
date=2022-05-04 time=09:42:28 logid=\"0100032001\" [...] from ssh(10.14.92.58)\" and then a final " to end the text field.
I do not believe FortiGate adds escape characters to the quotation marks when sending the message to Telegram API, so Telegram API is confused by the many quotation marks in the log message.
I can't say if this would require a feature request to fix or should be considered a bug, that needs to be decided by developers.
I would suggest opening a ticket with Technical Support and reporting the issue (as well as my theory) there to get some assistance in digging into the communication and figuring out if/how it can be fixed.
+++ Divide by Cucumber Error. Please Reinstall Universe and Reboot +++