If you are getting this error when you try to expand your storage spaces Vdisk, and you are using StorageTiers.

error extending volume size not supported storage spaces

you can expand your volume by using powershell instead

run the following command to get the names of your StorageTiers

Get-VirtualDisk <Vdisk FriendlyName> | Get-StorageTier | Select FriendlyName

In my case the name is VeeamVolume

Get-VirtualDisk “VeeamVolume” | Get-StorageTier | Select FriendlyName

and then expand the desired StorageTier

Get-StorageTier <StorageTier FriendlyName> | Resize-StorageTier -Size <Size>

Get-StorageTier VeeamVolume_HDD_Tier | Resize-StorageTier -Size 50TB

and after the resize

after StorageTier Resize

source: https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/resize-volumes