Problems recognition SD-card

I recently purchased the Vertex Nano 3D printer(VM8600).
Now my SD card is not recognized by the printer. The g code must be read in to calibrate the axes.
I have tried several cards, including reformatting.
I also followed and followed the instructions on the forum, which also did not help. (Init Card, change Card)

What can I do now to have the SD card recognized or do I need a specific Card?

How is the SD Card formatted?
Is must be in FAT32

Best Regards,

I have reformatted the card (FAT32) and rebuilt the files there. I also set up the spoolholder files. These are recognized. The CAL. STEP1.gcode and
CAL. STEP2.gcode is not recognized, even if I put them in a folder.

Best regards TonB

are they named
CAL. STEP2.gcode ?
please rename them to
cal_step2.gcode and cal_step1.gcode

The code is already in lower case, so it is downloaded.