If your state has a Licensing Board (like CA), they will tell you what the requirements are. It should be easy to look up on your state's website.... And usually (if you are a legitimate independent contractor - as defined by the IRS), your customer would or should want the Exemption for their own files and auditing purposes. Depending on your relationship with them, you may want to talk to their staff who handles the Insurance/Workers Comp stuff - they may be able to offer you some guidance in the right direction... (my primes have really been helpful in explaining why they need me to provide certain documents)
This is CABL.com posting #178059. Tiny Link: cabl.co/mUt5