Problems with sharepoint folder creation

Hello
I'm trying to port an Excel document with VBA macros, which I had developed for our network drives, to teams/sharepoint.
I am automatically creating folders based on the data that is entered. Unfortunately I now get the error message Runtime error '52': wrong file name or number.
Here is the code I use to check if a folder already exists.

Function CheckIfFolderExists(ByVal folderToCheck As String) As String
    CheckIfFolderExists = Dir(folderToCheck, vbDirectory)
End Function

Here also the value that is in folderToCheck: "\\xxx.sharepoint.com\sites\xxx\Shared Documents\xxx\xxx\001_01_de_SR_Test"
Why do I get this error? Do I perhaps make an error with the slash characters?

Thanks in advance

Seb