Hi Jess,
Thanks for posting your concern.
The reason why this error is occurring for working URL is because the
UrlFetchApp.fetch() and
getResponseCode() is not accepting some of the special characters.
With this, I would recommend using the encodeURI() function to decode the URL first before passing to the
UrlFetchApp.fetch().
For your convenience, you can clarify whether the Link checker you are using is for client account or MCC account so that I can point out the line of the code that needs to modify.
Regards,
Ejay
Google Ads Scripts Team

ref:_00D1U1174p._5004Q1zpGyH:ref