Please help me find the past registration/serial number of the aircraft

[OneOfTheCrowd]

https://www.jetphotos.com/viewqueued_b.php?id=10098783
I wrote in a comment for the screener that the msn is now unknown)))
I wrote in the appeal that they told me about msn on the forum. In response, I received "I agree with the rejection". Cool!

PS: I would be grateful if you tell me what is wrong with the contrast, I do not want to create a separate topic....

[OneOfTheCrowd]

Today I took a photo of an A320NEO S7 Airlines whose registration number changed a few days ago. I want to upload a photo to the site, but for this I need to find information.

Registration number RA-73448