I think I made it (hope, hope)

data/dbus/org.manjaro.pamac.conf

@@ -2,7 +2,6 @@
 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
 <busconfig>
-  <type>system</type>
   <!-- Only root can own the service -->
   <policy user="root">
     <allow own="org.manjaro.pamac"/>
@@ -10,10 +9,8 @@
 
   <!-- Allow anyone to invoke methods on the interfaces -->
   <policy context="default">
-    <allow send_destination="org.manjaro.pamac"/>
-    <allow send_interface="org.manjaro.pamac"/>
-    <allow receive_interface="org.manjaro.pamac"/>
-    <allow receive_sender="org.manjaro.pamac"/>
+    <allow send_destination="org.manjaro.pamac"
+           send_interface="org.manjaro.pamac"/>
   </policy>
 </busconfig>
 

data/dbus/org.manjaro.pamac.service

@@ -2,4 +2,4 @@
 Name=org.manjaro.pamac
 Exec=/usr/bin/start-pamac-daemon
 User=root
-
+SystemdService=pamac.service