Deleting Selected Input is not working perfectly, cannot figure it out

Hope this isn't too basic for StackOverflow, but other sites forums don't seem advanced enough to answer my questions which are a little over basic.

I'm trying to delete multiple selections, by adding the checkboxes on each listing and having one button for the entire form.

My test website is already hosted so you can view the real deal here: https://ift.tt/2jjsZPk

Please log in with "admin" (no password) and then you'll get to the cash-listing page. These are the listings I would like to delete, and as you can see, the checkboxes are there, but the button only works for one checkbox.

I done the research, and I tried to compare my code, and the code involved does match up. But my code is a little complex for me to find out exactly what I'm doing wrong. I'm new to PHP (started learning it 3 weeks ago!) so this might seem really basic to you guys. Please bare with me though, as you can see the rest of the website is my own work (proudly done with barely 3 weeks php and mysql knowledge!), I'm trying my best not to ask questions but this has got me really stuck. All the other buttons (delete, delete all, edit, add new, etc) are working very nicely. Only the delete-selected models is getting me stuck...

I'm not sure if you still need me to post the code snippets if I gave you the website link already, but if I do please let me know.

P.S. I already received downvotes for this question. Is it really such a crime to post a basic question on Stackoverflow?