ERROR 400: Invalid label name - invalidArgument

Full steps to reproduce the issue:
1. Google Takeout for mailbox file from old mail
2. use GYB to restore MBOX file to new mailbox

command used: gyb --email fietsenwarenhuisvanderveen@gmail.com --action restore-mbox --local-folder "C:\Users\Halfords\Desktop\googlebackup"

Expected outcome:
mailbox with folders and labels in new mailbox

Actual outcome (what errors or bad behavior do you see instead?
the error:
Restoring from 11.44gb file C:\Users\Halfords\Desktop\googlebackup\backup.mbox...
Creating label Gearchiveerd
400: Invalid label name - invalidArgument

Start with the restore-mbox action invoked by the reported gyb command and trace the label-creation request that returns “Invalid label name.” Reproduce the failure with the provided MBOX restore scenario, then verify that restoring the mailbox creates its folders and labels without the 400 error.

Written by the indexing model from the issue text.