Sorry - didn’t see you had replied! Here is what I’ve posted on another topic:
I can’t remember exactly what I did, but I know I applied for an FBI background check online from a private company located in America. I think I printed out their fingerprint form on card and took it to the main police station in the city where I live. I called ahead to check. They may have had a certain window I could go in, and I believe I had to pay in exact cash.
I did not fill in any online forms for the UK - I just called the closest major police station, paid in person and had them do my fingerprints. I then posted the fingerprints card along with the application form to that company in America.
I saved the receipts from both the application and the fingerprints and had the teaching agency I worked for pay me back. I chose to receive the results electronically in an email and via post. I think I may have had to have them posted to my parents in the US, as they did not ship to international addresses. I used National Background Check, Inc. Hope this helps.