EM7355 refuses to work

So I bought myself a WWAN card and as sierra has support for Linux I bought an em7355.
It arrived, I plugged it into my laptop, it is recognized, but I can’t use it (not even on Windows where I went through a driver hell to get it recognized.)
I can pass my PIN and unlock my SIM though.

I already dug around a bit. The serial ports are there, and I can talk to the using screen.
Using the Modem Manager CLI manually gives this error:

> mmcli -m any --simple-connect="apn=pinternet.interkom.de"
error: couldn't connect the modem: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Retry: Invalid transition'

This is all information mmcli gives me about the card:

> mmcli -m any                                             
  --------------------------------
  General  |                 path: /org/freedesktop/ModemManager1/Modem/1
           |            device id: <redacted>
  --------------------------------
  Hardware |         manufacturer: Sierra Wireless, Incorporated
           |                model: HP lt4111 LTE/EV-DO/HSPA+ Gobi 4G Module
           |    firmware revision: SWI9X15C_05.05.58.00
           |         h/w revision: EM7355
           |            supported: gsm-umts, lte
           |                       cdma-evdo, lte
           |                       lte
           |                       cdma-evdo, gsm-umts, lte
           |              current: cdma-evdo, gsm-umts, lte
           |         equipment id: <redacted>
  --------------------------------
  System   |               device: /sys/devices/pci0000:00/0000:00:14.0/usb1/1-8
           |              drivers: cdc_mbim, qcserial
           |               plugin: generic
           |         primary port: cdc-wdm0
           |                ports: cdc-wdm0 (mbim), ttyUSB0 (qcdm), ttyUSB2 (at), 
           |                       wwp0s20f0u8i12 (net)
  --------------------------------
  Numbers  |                  own: <redacted>
  --------------------------------
  Status   |       unlock retries: sim-pin (3), sim-pin2 (3)
           |                state: disabled
           |          power state: low
  --------------------------------
  Modes    |            supported: allowed: 2g; preferred: none
           |                       allowed: 3g; preferred: none
           |                       allowed: 2g, 3g; preferred: 3g
           |                       allowed: 2g, 3g; preferred: 2g
           |                       allowed: 2g, 4g; preferred: 4g
           |                       allowed: 2g, 4g; preferred: 2g
           |                       allowed: 3g, 4g; preferred: 4g
           |                       allowed: 3g, 4g; preferred: 3g
           |                       allowed: 2g, 3g, 4g; preferred: 4g
           |                       allowed: 2g, 3g, 4g; preferred: 3g
           |                       allowed: 2g, 3g, 4g; preferred: 2g
           |              current: allowed: 2g, 3g, 4g; preferred: 4g
  --------------------------------
  Bands    |            supported: egsm, dcs, pcs, g850, utran-1, utran-4, utran-5, utran-8, 
           |                       utran-2, eutran-2, eutran-4, eutran-5, eutran-13, eutran-17, 
           |                       eutran-25, cdma-bc0, cdma-bc1, cdma-bc10
           |              current: egsm, dcs, pcs, g850, utran-1, utran-4, utran-5, utran-8, 
           |                       utran-2, eutran-2, eutran-4, eutran-5, eutran-13, eutran-17, 
           |                       eutran-25, cdma-bc0, cdma-bc1, cdma-bc10
  --------------------------------
  IP       |            supported: ipv4, ipv6, ipv4v6
  --------------------------------
  3GPP     |                 imei: <redacted>
           |        enabled locks: sim, fixed-dialing
  --------------------------------
  3GPP EPS | ue mode of operation: csps-2
  --------------------------------
  SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/1

It looks like I got an HP-branded one. Would it help to remove the branding, if so, how?

My laptop is a Dell Precision 7510, currently running arch Linux (and Windows on an usb-hdd)

I finally managed to get it running. Was quite a journey.
I think the three main points I did was rebranding it to a generic device (don’t know the command anymore, unfortunately), flashing a generic firmware, and finally telling to accept the new firmware with AT!GOBIIMPREF.

The main reason it refused to work was this:

AT!PCINFO?
        State: LowPowerMode
        LPM force flags - W_DISABLE:0, User:0, Temp:0, Volt:0, BIOS:0, GOBIIM:1
        W_DISABLE: 0
        Poweroff mode: 0
        LPM Persistent: 0
        OK

but I’ve basically tried whatever I found on the internet to get it work, so there may be more steps that helped but didn’t ultimately make it work.

Good Luck with your own cards.