|I didn't get that solicitation. I'm already one of their vendors. I get their blast offers. I counter with my fee. Once in while, they agree and we do business. They require an invoice -- either USPS, email or through their platform. I usually invoice through their platform immediately upon completion of signing (or as soon as their system allows; sometimes, you have to wait 48 hours). Once in a great while, their invoicing system isn't working properly. At those times, I contact them and they give me an email address where I can submit my invoice using their template. They pay within 2-3 weeks via direct pay. Don't know how long it takes if you prefer a paper check.
There was a time they would call with offers. Their automated offers may be for low fees. We can counter-offer, and I do. If people would just stop accepting the low offers and counter with viable fees, we wouldn't be at this point. <sigh> Guess some people don't grasp the concept that this is a for-profit business and not a charity drive.