You can offer them an incentive for prompt payment or institute a penalty for late payment.  I knew one business that offered Air Miles to B2B customers but if they didn’t pay on time they didn’t receive the Miles.

For example, put a comment in bold at the bottom of the invoice.  New policy, prompt payment to terms will save you an additional 2% net off invoice, late payments will incur an additional 10% charge for xxx (name time frame) past the due date. Good Luck!