Employer is backpedaling on a verbal promise for commissions on my projects. Shame on me for not getting it in writing, it’s a small company and very informal. How can I be prepared when they say they never agreed to that even though my company President told me it was part of my new position?

New division of the company and I am the only employee doing most of the labor, 100% of my workload is things we have never done before. I was promoted in April with 6 months of salary negotiation. I was so exhausted of arguing by then that getting the % commission in writing fell by the wayside by then.