In addition to communication between the Sponsor and Principal Applicant, having proof of financial transactions between the couple will help solidify your relationship in the eyes of immigration officials.
This means that as soon as you enter a serious long-distance relationship with someone from another country – who may end up being a spouse or partner – you should keep any and all receipts of any transaction between the two of you.
Additional resource: How to prove your common-law relationship
Records of Gifts
Whether you’re legally married or common-law partners or even conjugal partners, any gift given or received or exchanged – for weddings, birthdays, or any other reason – should have its receipt stored away to be later used as evidence.
This might prove tricky in some cases if the gifts were given a few years ago and the receipts have been long discarded but try to scrounge up any you can find.
Gift receipts will always help.
Flight and other Travel Itineraries
Again, try to always print them.
If you didn’t print them at the time you travelled, contact the airline and use your booking reference number to see if they can email you the itinerary even though you have already travelled. If they do, then print it and use it.
Records of Money Transfers
You should include receipts of any money transfers between the two of you as part of your application to show financial support.
Assuming you used a well-known and reputable company (like Western Union for example) to transfer funds to your principal applicant (or the sponsor though this is less common) then you should contact them and ask for a copy.
For example, go here to Western Union’s customer care link to phone or email for a copy of your transaction if you sent your transfer by Western Union.
If you used another company to send your transfer, try the customer care page of the company you sent your transfer through to obtain a copy of your transfer receipt.