TopbarPlus v3.4.0 | Construct topbar icons with ease; customise them with themes, dropdowns, captions, labels and more

Don’t worry about that error. Just before you require the script make sure to do this

repeat
    task.wait()
until pathToYourIconModule ~= nil

Basically, that error pops up when the module fails to load. And the script I provided will just wait until the module isn’t nil (meaning is not unavailable).