PP Pro caught in Mask Rom Mode?

[nieral]

Hello!

A couple of days ago I wanted to try Postmarket OS again with my PP Pro, which I'm not using regularily. I flashed the latest image on the Sd card.

Since then I wasn't able to boot the phone again, no LED blinking, no vibration, nothing. First I thought I might have drained the battery.

So I tried the procedure mentioned here: https://wiki.pine64.org/wiki/PinePhone_P...ly_drained and charged the phone the whole night. Without success. 
It's not the battery as the battery works in my Pinephone.

What I already know:
- The image on the SD Card is fine
- The battery is working and charged
- none of the helpful procedure are working (i.e. holding volume up while powering the phone or try to bypass the emmc while booting up)
- there is the pre-installed image on the emmc (which isn't booting either)

What is strange:
As soon as I plug in the phone on my computer, it is shown in "mask rom mode" ("ID 2207:330c Fuzhou Rockchip Electronics Company RK3399 in Mask ROM mode") which shouldn't be the case if I'm not following the explicit procedure, right?

Anyone any idea?

Additional Information:
- Unfortunately I'm not sure which Bootloader is installed on the device. I ordered my PP Pro in March '22, but I believe I installed a different bootloader...
- I created the postmarket os image with pmbootstrap, using my laptop with fedora workstation. The image was written on the sd card with dd

[nieral]

I reinstalled Tow-Boot and tried a different sd card with a prepared image from postmarket os. And it worked.

[fxc]

I reinstalled Tow-Boot and tried a different sd card with a prepared image from postmarket os. And it worked.

For clarity, Maskrom Mode means the phone can't find anything bootable (eMMC, microSD) at all. So the issue here was not a drained battery, but a wrongly flashed eMMC and/or microSD card.