put external project into a cPack - cmake

Question

I try to setup a cMake project which create a package containing the output of multiple external projects. So the idea is, that I use this cMake project to create packages for the deployment.
Now the problem is, that when I use the cMakeLists shown bellow, the output of the external project is not included in the package. Just the internal one is in the package.
The install sequence of the external project seems to work, at least the output is in the install directory. It seams, that the package command doesn't see the binaries and for that reason dosn't put them into the zip archive.
Does anyone know, how to put the output of the external project into the package?
By the way: the external project is also cMake based. It contains a install step but no package step.
cmake_minimum_required (VERSION 3.12)
project(PackedBinaries
VERSION 0.0.42
)
set(GLOBAL_OUTPUT_PATH ${CMAKE_SOURCE_DIR}/temp)
include(ExternalProject)
# Builds external projects.
ExternalProject_Add(
myExternalProject
GIT_REPOSITORY "..."
GIT_TAG "master"
UPDATE_COMMAND ""
PATCH_COMMAND ""
SOURCE_DIR "${PROJECT_BINARY_DIR}/repo"
CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${GLOBAL_OUTPUT_PATH}
TEST_COMMAND ""
)
# Additional executable
add_executable(myInternalProject hello.c)
if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
set(CMAKE_INSTALL_PREFIX "${CMAKE_BINARY_DIR}/install" CACHE PATH "..." FORCE)
set(CPACK_INSTALL_PREFIX "${CMAKE_BINARY_DIR}/install" CACHE PATH "..." FORCE)
endif()
install(TARGETS myInternalProject)
install(DIRECTORY ${CMAKE_SOURCE_DIR}/temp DESTINATION "${CMAKE_BINARY_DIR}/install")
set(CPACK_PACKAGE_NAME ${PROJECT_NAME})
set(CPACK_PACKAGE_VERSION ${PROJECT_VERSION})
set(CPACK_PACKAGE_VERSION_PATCH "0")
set(CPACK_PACKAGE_INSTALL_REGISTRY_KEY ${PROJECT_NAME})
set(CPACK_GENERATOR "ZIP")
# Must be after the last CPACK macros
include(CPack)