Error: setSecret: Unable to log into database with previous, current, or pending secret when configu

I created a rotation Lambda manually by using MySQL template, after kicking off the rotation, it gave me error:

[ERROR] ValueError: Unable to log into database with previous, current, or pending secret of secret

I found this solution and tried but doesn't work (I'm not very sure about step 2 though, about where to store the file 'latest RDS CA Bundle'), what I did was put in the folder and zip again, uploaded to Lambda.

In addition, I don't know if I'm using the right Lambda template for rotation, what's the difference between 'Single user'and 'Multiple user'? I thought my secret only contain one user and one password so I used the template for one single user, is that correct?

I've spent a very long time on this whole rotation thing, this has already took me way too much time than I expected! Really exhausted... Can anyone help me... Thank you.