SQL Server 2016 SP1 Managed Backup to blob storage
While Microsoft corrects this bug in SQL 2016 a workaround is the following:


Create a credential to your azure storage but use an Access Key as password instead of a SAS (this was the procedure for SQL 2014). 
Enable the Managed Backup (it will work correctly)


At this point MB is enabled but backups created by it (and any manual backup using the same storage) will fail because of the credential being created in 2014 mode, so


Modify the credential changing the Password to the SAS.


Now backups will start to run.
If you need to disable or configure MB again you will have to switch to Access Key and then back again to SAS.