Is USA service dogs legit?

Hey everyone, I want to know if is a scam. I’m trying to register my dog as an emotional support animal, and they’re telling me I need to get an ESA letter. They said a therapist will contact me, but I’m feeling unsure because they want payment upfront.

There’s a lot of information online about fake service animal registrations, and I don’t want to fall victim to a scam.

Can anyone recommend a reputable way to obtain a legitimate ESA letter?