We have found an issue with the + sign character in zoho subs - we are allowed to create a customer with an email address that has a plus sign but the API doesn't allow the + so the billing portal is not created.     We are going to prevent users from using an email address with a plus sign so this we don't have this issue.

What other characters might cause similar issues in either the app or when using the API?     What is a safe character set that we can implement in our front end validation so we don't run into any issues like this moving foward?