If you are using the Cross-tenant OneDrive migration service offered by Microsoft to migrate users OneDrive content from one Microsoft 365 tenant to another, in rare cases you might find yourself receiving this error when you try to create the trust between the two tenants:
It has been detected that partners reside in the same SPO location that prevents them from migrating. Please contact MS to resolve this issue. Once the issue has been resolved, please try running the migration again.
This error means that both the source and target tenants have their SharePoint data being hosted on the same farm. This should be rare because even if both tenants are in the same geographical location, for them to both be hosted in the same SharePoint farm is … unlucky.
As the error message states, to fix this you will need to raise a ticket with Microsoft support. They will arrange with the SharePoint engineering team to migrate the data of one of the tenants to another farm. I recommend checking which tenant has the least amount of data in SharePoint and suggesting to the support representative that they migrate that one. You should also identify if this issue exists (by running the commands to create the tenant trust) as early as possible, because after you raise the ticket, it can take several weeks to be resolved. It took two weeks to resolve for me and that was with a small tenant. I imagine for tenants with more data it could take longer.
Kevin's tech blog 