Error setting outages

[david-delco]

Good morning,
In using your interesting plugin I encounter the errors I post below (Moodle 3.7+). I set it up from the Administrator menu in Moodle.
Yesterday I had accidentally set parameters and got locked out of the platform so I ran the plugin shutdown from CLI.
I don't know exactly what it is, because moreover now it would seem to work, but I noticed that if I enter the placeholders "start" "duration" and "stop" they are not considered (only duration works).
Is this a problem or am I doing something wrong? Yet I seem to have followed the instructions to the letter.
Error in image 1

Today I tried to uninstall the plugin but I get the error in image 2

Could you please tell me if the installation of this plugin can in any way affect or interfere with the operation of other plugins?

Thanks for any help.
David