ERROR: Could not generate cargs for wingpanel-2.0

[Net-Felix]

when i try to build i get the following error:

The Meson build system
Version: 0.48.2
Source dir: /home/felix/wingpanel-indicator-dropbox
Build dir: /home/felix/wingpanel-indicator-dropbox/build
Build type: native build
Project name: com.github.isneezy.wingpanel-indicator-dropbox
Project version: 0.1.0
Native C compiler: cc (gcc 7.3.0 "cc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0")
Native Vala compiler: valac (valac 0.40.11)
Build machine cpu family: x86_64
Build machine cpu: x86_64
Found pkg-config: /usr/bin/pkg-config (0.29.1)
Dependency wingpanel-2.0 found: NO 

meson.build:17:0: ERROR:  Could not generate cargs for wingpanel-2.0:

but i think it is installed:

sudo dpkg -l | grep -i wingpanel
ii  libwingpanel-2.0-0:amd64                   2.2.0+r243+pkg37~ubuntu5.0.1                   amd64        A super sexy space-saving top panel
ii  libwingpanel-2.0-dev                       2.2.0+r243+pkg37~ubuntu5.0.1                   amd64        Library to build plugins for WingPanel (development files)
ii  wingpanel                                  2.2.0+r243+pkg37~ubuntu5.0.1                   amd64        A super sexy space-saving top panel
ii  wingpanel-indicator-bluetooth              2.1.1+r172+pkg23~ubuntu5.0.1                   amd64        WingPanel Bluetooth Indicator
ii  wingpanel-indicator-datetime               2.1.2+r313+pkg17~ubuntu5.0.1                   amd64        WingPanel Date & Time Indicator
ii  wingpanel-indicator-keyboard               2.1.1+r172+pkg24~ubuntu5.0.1                   amd64        WingPanel Keyboard Indicator
ii  wingpanel-indicator-network                2.2.1+r403+pkg21~ubuntu5.0.1                   amd64        WingPanel Network Indicator
ii  wingpanel-indicator-nightlight             2.0.1+r103+pkg6~ubuntu5.0.1                    amd64        WingPanel Nightlight Indicator
ii  wingpanel-indicator-notifications          2.1.2+r237+pkg20~ubuntu5.0.1                   amd64        WingPanel Notifications Indicator
ii  wingpanel-indicator-power                  2.1.3+r324+pkg17~ubuntu5.0.1                   amd64        WingPanel Power Indicator
ii  wingpanel-indicator-session                2.2.1+r282+pkg15~ubuntu5.0.1                   amd64        WingPanel Session Indicator
ii  wingpanel-indicator-sound                  2.1.1+r228+pkg16~ubuntu5.0.1                   amd64        WingPanel Sound Indicator

[isneezy]

Hello, I'll try to help but do note that I'm not a guru. this is my first package into the linux world!
could you post here the output of the pkg-config --cflags wingpanel-2.0 command? also please post the contents of cat /home/felix/wingpanel-indicator-dropbox/build/meson-logs/meson-log.txt

[Net-Felix]

Ohh, shame on me!
i forgot to install "libgtk-3-dev"

now everything is fine ^^