Formula using mid and length not working in the last part of formula - but not sure why

[mightybracket123]

Hi all,

I'm tring to combin the MID and Length function to remove text both at the start and end of some text.

The text in my real document always starts with the same 18 characters which I need to remove - and I can get the formula to do that. But then I also need to remove the very last character of the text and I just can't get the formula to remove that last character, but I'm not sure what I'm doing wrong.

I've spent hours googling this and just getting no where and wondered if anyone had any ideas on where I am going wrong?

The example I've attached shows how the text in my spreadsheet is structured, the formula I'm using, the result I get vs what I would like to achieve.

Any advice would be much appreciated.

Thanks in advance to anyone who has time to look at this. !