A grader feedback with series_valid not defined points either you are using incorrect functions or mixing global variables with local variables. Here is a post with 3 solutions which should help you debug your codes. While passing unittest is related to grade function codes but doesn’t always confirm one would pass the assignment grader.
Let me know if you’re still stuck. Also as you are posting first time a query, just for you information posting any of the codes from grade function code in public post is not allowed and considered violation of Code of Conduct. If a mentor wants to see your codes, they will ask you to send them by personal DM.
Regards
DP