@Erin Davis Firstly, apologies for the delay in responding here and any inconvenience this issue may have caused.
For better understanding the issue : Are you using the same blob in task scheduler and PowerShell?
- Are you using the differential backup instead of a full backup?
- Can you share the screen shot of the error message?
- Which version SQL Server are using?
- Additional information: This error may also arise if the SQL Backup Agent service doesn't have the necessary permissions. For example, if you are restoring across a network, the SQL Backup Agent service must have read permission to access the folder containing the backups. For more information on the permissions required by the SQL Backup Agent service, check Permissions once
(If the reply was helpful please don't forget to accept as answer, thank you)