Dell Repository Manager - Cannot create custom Smartbootable ISO

We have a requirement to update a number of R740 and R740xd servers to a consistent firmware level prior to installation of ESXi. We don't have OMEE in the environment at the moment.

I have downloaded the relevant catalog file from the Dell support site for the version of ESXi we are using from this url :

https://www.dell.com/support/article/uk/en/ukbsdt1/sln311042/firmware-catalog-for-dell-customized-vmware-esxi-images?lang=en

I have then created a new repository and used the XML catalog file as the source. I have selected R740 and R740xd as the server models and all operating systems and components.

The repository creates successfully and the components are downloaded but when I try to export the repository to a Smartbootable ISO I get an error message 'Selected repositories/bundles are not valid for this deployment'.

Any idea why I get that error ? I can create a SUU ISO instead successfully, would I be able to use that to update the firmware using the Lifecycle Controller instead ?

If so can I make the SUU ISO with all the components on the catalog, and will the Lifecycle Controller detect the exact components in the system, update those and ignore the rest ?

Many thanks, James