One issue that I, as a developer for 3rd party clients, run into is getting the CSR submitted and domain verified. Each 3rd party SSL provider works different and they usually will only send the CRT after verifying your client owns the domain. In the past I had only used email verification which has to go to some name in the WHO IS for that domain. Sometimes that is easy and sometimes the email is some web developer for the company or a 3rd party contractor that is hard to get a hold of or sometimes it is going to an email that no one knows who receives it such as email@example.com. So it can be a hassle seeing who receives the confirmation email so that you can click a verification link in that email to prove you control that domain.
Many SSL providers will give you an alternative to email verification by letting you post a file they send you on your web site and if they see it on your web site, they will know that you own that domain because you put it there. FileMaker takes over web services and just because you have a domain for your machine, you don't know where to put this file on the root of the web page so it shows up like http://yourfilemakerdomain.com/verificationfile.txt In other words, the location is not the normal default web root location.
If you need to know where to put this verification file for verification, here are the locations:
[drive]:\Program Files\FileMaker\FileMaker Server\HTTPServer\htdocs\[verificationfilename]
Just substitute the actual file name where it says [verificationfilename]
So for my client's Mac server, I put it at /Library/FileMaker Server/HTTPServer/htdocs/verificationfile.txt and I can see it on the web in a web browser by going to http://myfilemakerdomain.com/verification.txt
Once they verify the file is there, they usually will email you the CRT file and you can import the certificate into the FileMaker Server. Or you may have to log into their web site to get the CRT. Either way you are good to go.