Cannot connect to the database V1.5.5

Hello
I want to install version 1.5.5 but I have this erratic message?

Do NOT create multiple threads for the same topic!
https://community2.invoiceplane.com/t/topic/5413/1

This is your last warning. We have rules in this community everyone has to follow. If you do not get an answer, wait. This is not a paid software with paid support staff.