You've made that mistake in other places as well:
Billing.ClientID, Billing.RateID, BillingStaffID are text, should be number
Billing.BillingDate is Text, should be date
You need to use the correct data type for your data.
You should make your autonumber fields primary keys. Right click and then click on "Primary Key" in design view of the table.
And only use alphanumeric and underscore characters in table/field names. That means no spaces (e.g. [Postal Code] = [PostalCode])
Lastly, tables with only 1 real data field (autonumbers don't count as real data) shouldn't exist. Your Rates table should go. Instead of storing the RateID value in Billing you just store the actual rate value.