PHP: send array as form post input parameter

I have a pre-defined array. I'd like to send it with an HTML form:

The form submits to the same page.
I get the output:

If I comment out the last two lines in the try statement:

I get:

I'd like to get output:

How should I change the code to get it?
EDIT:
I changed the code to

now I get this output:

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