Failed to insert an entity in kong-db when following the docs

Hi all,
I followed:Storing Custom Entities - v3.5.x | Kong Docs. But failed to insert a n entity in the db.
I just follow the docs above and I did not edit any code in the docs. When I try to insert an entity, I only get ‘curl: (52) Empty reply from server’ from kong. How can I know what cause this problem? can you help me?
Here is my step:
I follow the docs and create the ‘daos.lua’ and ‘migration’ folder:
The code in the .lua files is the same as docs.
Last, I try to insert entity as follows:

and I only get :