Each wallet that purchases an NFT receives a username with a corresponding referral link. Your username is what links you to other NFTs in the matrix and creates a primary position.
When someone clicks your referral link and enters the MetFi app for the first time your username is stored on their device’s browser. If they then purchase an NFT in the same browser, your username is the referee and they will be placed in your matrix.
The referral link cannot be overwritten in the same device browser even after clicking another referral link at a later time. Doing so will default to the first referral link that was used to enter the MetFi app making the first referral link they clicked the referee even if they terminate the first browsing session or clear cookies. After the user buys an NFT the referral link is cleared from the device and they will be able to use another referral link on the same device and browser.
You can change your username at any time, and as often as you like, but doing so also changes your referral link. If you have previously shared your referral link before changing it, the old referral link will no longer work and you will no longer be the referee if a person clicks it to enter the MetFi app.
Changing usernames has no impact on any members that are already in your matrix. As stated above, once an NFT is placed in a matrix it is forever locked in that matrix and will remain permanently connected to your NFT, no matter how many times you change your username.
Two other methods of binding an NFT to your NFT and your matrix are to gift an NFT using the internal gifting feature in the app, and the other is for an NFT purchaser to type your username if prompted to enter one while completing their first NFT purchase.