Non-Payment Contract Dispute Resolution

I'm facing a serious issue regarding a contract with a client. The contract pertains to extra advertising usage on a model. The primary concern is a payment dispute, specifically related to non-payment for the extra advertising. I need an experienced professional who can help me navigate this dispute and hopefully resolve it in a timely manner.

Ideal Skills:
- Contract Law Expertise
- Negotiation Skills
- Dispute Resolution Experience
- Advertising Industry Knowledge
- Client Management Skills