Can't create formula always get error

Can't create formula always get error

HI there,

I'm trying to create a custom Deal layout, and one of its fields it has to be a sub-string of the account name (the first 3 characters, let's say the Account name is JackDoe the sub-string will be Jac), so the formula goes like this:

Substring(${Deals.Account Name} , 1 ,3 )

and I get: Make sure you choose a Formula Return Type that matches the type of data your formula produces. (e.g. If your formula returns a string, then you should choose a Formula Return Type. string)

So I tried:

Substring( Tostring(${Deals.Account Name}) , 1 ,3 )

and also get the same error.,.. any ideas?

Also, is there a way to have an automatic incremental number? So every time I create a deal I have this auto number as a unique code, also combined with the sub-string, so the deals codes would be JAC001, JAC002, JAC003.

Thanks!