When attempting to provision a user's OneDrive site, Sharegate displays the following error message:
The SharePoint server took too long to complete the provisioning. The One Drive site will still be provisioned, but it could take some more time.
The error occurs because provisioning the user's OneDrive is taking more than 5 minutes. This doesn't mean the provisioning won't happen, just that it's taking more time than expected.
You can try running the provisioning command again in a few more minutes to check if it has finally been provisioned or to send the provisioning request again if it hasn't.
If it still isn't provisioned after an hour, try having the user log into https://tenantname-my.sharepoint.com and provisioning it manually. If it doesn't work, contact Microsoft support directly as there may be a problem with the user's OneDrive.