Technically speaking, an RFE is a written request for more information and documentation that USCIS mails out if they believe that they don’t yet have enough evidence to approve or deny a given application. An RFE normally is a minor item and should not be looked at like it's a denial but an opportunity for you to complete your application. USCIS would not send out an RFE if they were going to deny your application. It's just a step that they must take and once they have your information and it meets their approval then you should be seeing your NOA2.
There are many varying degrees of RFE's. Some as simple as not "ticking" off a question. Others forgot the fiancé(e) letter and then others who met on a website and now need to prove that it wasn't a marriage arrangement website.
Once you get your RFE, read over very carefully as you only have one chance to reply accurately without causing undue harm. Once you know FROM THE RFE what it is set out to correct and to include "everything" they are asking for. Then reread the RFE to ensure you are compliant. Make copies of everything for your record and send back using their instructions which are contained within the RFE. If the RFE requires a signature, PLEASE don't forget this. Include the original RFE letter along with a cover letter explaining what you are including in your reply. Like a checklist format. Use the envelope that is provided for the return of your RFE. Once received at USCIS your case will begin adjudication where the agent had left off. No one can tell you how long it will take so be patient.
Congratulations! Join us in the DECEMBER 2020 K-1 NOA2 to NVC to EMBASSY thread and download the PDF file on the first post of the first page for tips, tricks and hacks to follow your case to the embassy. I'll post both links below: