There are different places where you will see different errors.  The only listing that I can think of are the errors associated with Web Hooks: https://help.docebo.com/hc/en-us/articles/360020124499-Webhooks-Error-Management

For errors that users would see:

I can for sure say, if a user reaches out to you saying they are seeing a 403 error, it is because they are trying to access a page they are not allowed visibility or they were given a direct URL to a course that they were not enrolled in.

I’m trying to remember, either a 500 or 505 error is something wrong on Docebo’s side and I have opened tickets before to remedy those.

Maybe others can sound out below on errors they know and then we can begin a nice list here!

Agree with you @Annarose.Peterson the most common error codes are 403 & 500 where 403 is an access error that an admin can usually resolved and the 500 is a network type error. These codes should be fairly standard.

found this that should be helpful...it has many more codes than we usually see but it does contain the 403 & 500 codes

https://developers.google.com/webmaster-tools/v1/errors