The user is not able to add sites using the Vault Loader.
The user is using in_migration__v as the status for the sites being added in the Vault Loader input file. There are no active Archived Site licenses available in the affected Vault.
Using in_migration__v as the status for the affected sites as part of a Vault Loader site addition job results in those sites being licensed as Archived Sites.
The solution is to update the status for the affected sites in the Vault Loader input file to active__v so that they are added as Active Sites.
Vault Loader Documentation: About Vault Loader