Ensure your client has signed the contract, or you have their signature/approval recorded on another document.
The benefits of the online signature is a timestamp is recorded as soon as they sign.
Keep a record of all conversations through email or text. It is difficult to submit evidence without a timeline.
Proof of Event
Have your clients sign the Receipt of Goods and Services upon receiving the items.
Keep all signed documents or proof of the event (photos, testimonials, etc) in the Files section of the Project.
If a dispute is reported, first reach out to your client to confirm they issued the dispute purposefully.