The rule: A singular subject gets a singular verb, a plural subject gets a plural verb
What’s the subject in this sentence? A list of customer accounts has three items.
It’s “list,” even though the verb is right next to a plural noun. So the singular noun gets a singular verb, “has.”
Here’s a tricky one: We have here a list of items that occur/occurs in an error condition.
Is it the list that occurs, or is it the items that occur?
It’s the items!
Be alert for what the subject is! It can make a big difference in what you say.