Hey Jake. Sometimes when copy-pasting, some whitespace characters can sneak in there, especially at the start/end. Try pasting into a plain text editor first (e.g., TextEdit or Notepad), just to make sure that there aren’t any hidden characters.
Depending on where you originally copied the seed, there (unlikely, but plausibly) might be some non-printable characters hidden in there as well. These characters will mess up your seed, and they’re impossible to spot in a text editor.
Depending on your level of regex-fu, you may be able to throw together a script to replace the invalid characters with
9, or ask around on the IOTA Slack for assistance.