How to combine or merge cells, using php-codeigniter

Hello, im using codeigniter and php to create this table.

im using collapse from bootstrap to view childrow like datatable can do. but i dont understand to use js, so im using only php here. the childrow is a new row with only 1 td, and that causing error

is there any solution to make childrow using only php?
from what i know, if you want to merge cells in php you only create 1 td with colspan=12, but datatable not allowing that..

here is when im creating the td with no value

here is when im deleting the td and causing errors

and the attachment file is the code that i wrote