Welcome to our community 
Unless someone here comes up with a trick unknown to me yet, please clarify if you can send and receive anything (or more specifically, your FP4) to/from France at all right now. Quite directly, I am confident someone in this community might actually be willing to help out with the payment issue (right now I won’t promise it myself, but I might discuss it with my local Fairphone Community here in the next days).
Update: Did you check with Fairphone Support if Fairphone’s France repair centre would even accept an FP4 send-in from Ukraine? This Support article suggests they do not service your country 
https://support.fairphone.com/hc/en-us/articles/202005103