Hey Jen!
So I'm no expert, but I did submit "evidence of financial support" with my original petition as further proof of relationship - only because my beneficiary is from Nigeria and I wanted to frontload our application with as much evidence as possible to show that its a real and bonafide relationship, anyway what I submitted was proof of financial transactions. So various times I sent him money or purchased gifts for him / us. I included bank statements that showed the money transfers or items purchased, as well as text conversations where maybe he thanked me for sending money or acknowledging receiving it and I included descriptions with the month + year and explanation for what they were looking at.
example:
Date: January 20206
Description: My beneficiary and I decided to start marriage counseling together. So I purchased the books we would read for our marriage counseling course.
Then I'd include an image of my bank statement showing the purchase, the receipt from amazon also showing the book i bought, and maybe a text conversation where he and I are talking about the book, or where hes saying hes excited to start reading it together etc etc.
I still havent gotten NOA2 yet, im waiting... so I cant say that what I did was "correct" or the way to do it. But its what I did if you need some ideas. But honestly, if I got a RFE that asked for proof of financial support, Id cover all my bases and send proof of times I sent money or gifts, as well as the I-134 form, and my tax paperwork to prove I also meet the threshold. I just wouldnt take the chance to make any mistakes in case that is what they are asking for.
I hope this helps!
I also got a ton of ideas watching this YT channel, Goodluck!
https://www.youtube.com/watch?v=3HjOFYTTjAc