Getting ready to do a Box to SharePoint/OneDrive migration using the M365 built-in migration tool. We will be migrating to 900+ unique OneDrives, and another 400+ SharePoint locations as part of this effort. Pointing and clicking to map 1300 different entries to each of their locations was not something anyone on the team wanted to do.
But we were having the strangest issue with the Mapping Destinations tool. Read through the documentation multiple times, and could not figure it out.
The issue was that none of our upload attempts would take. We would follow the steps - download the MigrationDestinations.csv file, fill in the Destination Path column, and then upload. After uploading, all of our destinations continued to just say that they were not mapped.
I've used this tool a few times before, and never had this issue before.
After hours of research and combing through discussion groups, I finally figured out the issue. The usernames in this environment were all of the LastName, FirstName format. This column, which appears at the beginning of the downloaded mapping template file, was throwing off the rest of the file because it had a stupid comma in it.
So if you run into this issue yourself, and you cannot figure out why your mappings are not taking, just do a Find/Replace in Excel on Column A of the mapping file, removing all of the commas from it.
Hoping this post saves someone moving forward from banging their head against the wall on this.