Error while following the SDK livery example

When doing this tutorial:

https://docs.flightsimulator.com/html/index.htm#t=Samples_And_Tutorials%2FTutorials%2FCreating_A_Livery_Package.htm

It always ends up with a build error

AssetBuilder | Could not find a valid simobject in 'L:\My Drive\MSFS\Projects\TestLivery\PackageSources\SimObjects\Airplanes\pieter-test-livery'. 
Does it have one of [aircraft.cfg / sim.cfg / container.cfg] and does it reference the correct model folder(s)?

The folder does have an aircraft.cfg file:

[VERSION]
major = 1
minor = 0

[VARIATION]
base_container = "..\Asobo_C172sp_AS1000"

;===================== FLTSIM =====================

[FLTSIM.0]
title = "Cessna Skyhawk G1000 Asobo - Test" ; Variation name
model = "" ; model folder
panel = "" ; panel folder
sound = "" ; sound folder
texture = "test" ; texture folder
kb_checklists = "Cessna172SP_check" ; Procedures/Checklist sibling file name
kb_reference = "Cessna172SP_ref" ; Reference information sibling file name
description = "TT:AIRCRAFT.DESCRIPTION" ; Variation description.
wip_indicator = 0 ; know if the variation is good to go or still WIP : -1=Disabled, 0=Rough, 1=1st Pass, 2=Finished
ui_manufacturer = "TT:AIRCRAFT.UI_MANUFACTURER" ; e.g. Boeing, Cessna
ui_type = "TT:AIRCRAFT.UI_MODEL" ; e.g. 747-400, 172
ui_variation = "TT:AIRCRAFT.LIVERY.DEFAULT" ; e.g. World Air, IFR Panel
ui_typerole = "Single Engine Prop" ; e.g. Single Engine Prop, Twin Engine Prop, Rotorcraft, etc
ui_createdby = "Asobo Studio" ; e.g. Asobo Studio, Microsoft, FSAddonCompany, etc
ui_thumbnailfile = "" ; app relative path to ThumbNail image file
ui_certified_ceiling = 14000 ; service ceiling / max certified operating altitude (ft)
ui_max_range = 640 ; max distance the aircraft can fly between take-off and landing in (NM)
ui_autonomy = 5 ; max duration the aircraft can fly between take-off and landing in (Hrs)
ui_fuel_burn_rate = 54 ; average fuel consumption per hour (lbs/hr) - reminder: fuel density is ~6.7lbs per US gallon
atc_id = "ASXGSA" ; tail number
atc_id_enable = 1 ; enable tail number
atc_airline = "" ; airline name
atc_flight_number = "" ; flight number
atc_heavy = 0 ; heavy?
atc_parking_types = "RAMP" ; "ANY" / "RAMP" / "CARGO" / "MIL_CARGO" / "MIL_COMBAT" / "GATE" / "DOCK"
atc_parking_codes = "" ; Comma separated and may be as small as one character each
atc_id_color = "" ; color for the tail number : i.e. "#ffff00ff"
atc_id_font = "" ; font for the tail number
isAirTraffic = 0 ; Is the plane usable for air traffic
isUserSelectable = 1 ; Is the plane selectable by the user

The contents of
L:\My Drive\MSFS\Projects\TestLivery\PackageSources\SimObjects\Airplanes\pieter-test-livery:
image

The contents of texture.test:
image

The contents of texture.cfg:

[fltsim]

fallback.1=..\..\Asobo_C172sp_AS1000\texture

Does anybody have any idea why this is failing? I’ve been trying various things now for 2 hours (started over, different planes, 3rd party planes, etc) and always the same error message. Like it doesn’t detect airplane.cfg or doesn’t get the base_container part, while I’ve seen it working fine with other (compiled) liveries.