How to generate rbf file for u-boot "fpga load" on Agilex7/SDM

I have a project_hps.sof file which I'm able to load using quartus_pgm, but I would like to convert this to rbf and load it from u-boot.

I usually do:

quartus_pfg -c -o compression=on project_hps.sof project_hps.rbf

But this results in an error on my A2700 board:

SOCFPGA_AGILEX # crc ${loadaddr} ${filesize}
crc32 for 02000000 ... 02189fff ==> 6eef0981
SOCFPGA_AGILEX # fpga load 0 ${loadaddr} ${filesize}
..Error sending bitstream!
Command 'load' failed: Error -110

The crc32 is the same I get on the rbf on the server side so I know the content is correct. But "fpga info" tells me:

SOCFPGA_AGILEX # fpga info 0
Altera Device
Descriptor @ 0x000000007ffdc790
Family: Intel SDM Mailbox
Interface type: Secure Device Manager (SDM) Mailbox
Device Size: -1 bytes
Cookie: 0x0 (0)
No Device Function Table.
SOCFPGA_AGILEX #

Is the problem related to MSEL settings or do I have to add encryptions keys to the rbf somehow since the interface type is "Secure Device Manager (SDM) Mailbox" and not "Fast Passive Parallel" or similar?