Could you please share the error message? And your mapping export?
I figured out a way to accomplish what I want to do. But I'm not sure if it is the best way.
I start out by creating a variable port, v_my_port_array, of type array whose type is string and use the ARRAY function to convert the dynamic port,From_Read_My_Table_specificPortSelection, to an array. All of the ports in my dynamic port are strings.
v_my_port_array = ARRAY(From_Read_My_Table_specificPortSelection)
Next I create another variable port, v_my_port_string, and use the CONCAT_ARRAY function to convert my array port to a delimiter separated string. I specified my delimiter as '' so I don't have any extra characters when applying the MD5 function later.
v_my_port_string = CONCAT_ARRAY('', v_my_port_array)
Last I create an output port, o_my_port_md5, of type string and apply the md5 function to v_my_port_string.
o_my_port_md5 = MD5(v_my_port_string)
I ended up having to work this out in steps, as in, create each of the variable ports rather than nesting functions. When I tried nesting these functions I would get run-time errors, although the mapping would validate.