Building the Linux client libraries fails because of missing files

I downloaded and installed the Nakama source code from here: Releases · heroiclabs/nakama-cpp · GitHub

Unpacked it on Linux and successfully run install_deps.sh

Then I try to build Nakama but it fails:

~/svn/nakama-cpp-2.5.1/build/linux $ python build_linux.py
BUILD_REST_CLIENT = True
BUILD_GRPC_CLIENT = False
BUILD_HTTP_CPPREST = True
BUILD_WEBSOCKET_CPPREST = True
BUILD_C_API = True
BUILD_NAKAMA_TESTS = True
copied nakama-cpp
copied nonstd
copied nakama-c
copied nakama-cpp-c-wrapper
Architecture: x64
Build mode  : Release
Shared object: False
calling: ['cmake', '-B', '/home/andreas/svn/nakama-cpp-2.5.1/build/linux/build/Release_x64', '../..', '-DCMAKE_BUILD_TYPE=Release', '-DNAKAMA_SHARED_LIBRARY=OFF', '-DBUILD_REST_CLIENT=ON', '-DBUILD_GRPC_CLIENT=OFF', '-DBUILD_HTTP_CPPREST=ON', '-DBUILD_WEBSOCKET_CPPREST=ON', '-DBUILD_C_API=ON']
CMake Error at CMakeLists.txt:75 (add_subdirectory):
  add_subdirectory given source
  "/home/andreas/svn/nakama-cpp-2.5.1/third_party/grpc/third_party/boringssl-with-bazel"
  which is not an existing directory.


CMake Error at CMakeLists.txt:77 (add_subdirectory):
  add_subdirectory given source
  "/home/andreas/svn/nakama-cpp-2.5.1/third_party/grpc/third_party/protobuf/cmake"
  which is not an existing directory.


-- Setting gcc options
CMake Error at third_party/cpprestsdk/Release/cmake/cpprest_find_websocketpp.cmake:14 (message):
  -- websocketpp not found and embedded version not present; try `git
  submodule update --init` and run CMake again
Call Stack (most recent call first):
  third_party/cpprestsdk/Release/src/CMakeLists.txt:68 (cpprest_find_websocketpp)


-- Configuring incomplete, errors occurred!
See also "/home/andreas/svn/nakama-cpp-2.5.1/build/linux/build/Release_x64/CMakeFiles/CMakeOutput.log".
See also "/home/andreas/svn/nakama-cpp-2.5.1/build/linux/build/Release_x64/CMakeFiles/CMakeError.log".

When checking the folder /home/andreas/svn/nakama-cpp-2.5.1/third_party/grpc it is empty…
Any idea?