conditional formatting help please

[Rogerisit]

Hello!
In column B I have invoice numbers, but not on every row due to some invoices having multiple items, (row d- irrelevant) and in column C I have the date the invoice was sent. What I'm trying to do it highlight the invoice numbers in column B if there is no date in column C. I would like help with what I'm assuming is an IF formula to make this happen.
Thanks kindly

 

[oldbrewer]

=c2="" in b of course

 

[Rogerisit]

Thank you, I truly appreciate your help. This works except that the blanks in column B are also being highlighted.

 

[oldbrewer]

let b2="" and C2 =""

b2 can only turn eg red if C2=""

if you only want b2 to turn red if b2 is not blank and c2=""

then =and(b2<>"",c2="")