installed library contains call to non-existent luaL_register

[HJarausch]

Hi,
I am new to Lua. I have lua 5.3.5 and luarocks 3.1.3 installed on my Gentoo system.
Invoking
luarocks install lmapm
generates and installs the library
/usr/lib64/lua/luarocks/lib/lua/5.3/mapm.so
which refers to luaL_register which doesn't exist in Lua 5.3 any more.

Here my commands
export LUA_CPATH=/usr/lib64/lua/luarocks/lib/lua/5.3/mapm.so
lua
Lua 5.3.5 Copyright (C) 1994-2018 Lua.org, PUC-Rio

mp=require("mapm")
error loading module 'mapm' from file '/usr/lib64/lua/luarocks/lib/lua/5.3/mapm.so':
/usr/lib64/lua/luarocks/lib/lua/5.3/mapm.so: undefined symbol: luaL_register

I find it strange that setting
LUA_CPATH=/usr/lib64/lua/luarocks/lib/lua/5.3
gives an error saying that LUA_CPATH points to a directory which should be the normal case for a 'PATH'.

What am I missing?
Many thanks for a hint,
Helmut