Hi all, hoping someone can help me with a little trouble I'm having.

Order numbers in our system always begin with a letter "O" followed by 7 numbers (eg O6277305)

I have a sheet where users enter order numbers and I want to use custom data validation on this column so that you get an error if:
a) It doesn't begin with the letter "O"
b) It doesn't contain 8 characters
c) It contains any spaces

I have figured out how to do each of these by themselves (as below) but I can't seem to get them to work all together.
a) =LEFT(B3,1)="O"
b) =LEN(B4)=8
c) =B5=TRIM(B5)

I have tried the below, which data validation seems to accept is a legitimate formula but I don't get an error when entering something that breaks the rules:
=AND(LEFT(B3,1)="O",LEN(B4)=8,B5=TRIM(B5))

Is anybody able to give some advice on what I might be doing wrong?

Many thanks,
Luke