From the code on your order to wallet funds on your PSN account, on console or in the app.
Go to redeem.microsoft.com in any browser, or on your console press the Xbox button, then Store, then Redeem. The web route is the fastest and works for PC and console alike.
Credit lands on the account you are signed in with, and it cannot be moved afterwards. If you share a console, double check the profile picture in the top corner before you continue.
Open your order on Keeoto and press Reveal. Copy the code rather than typing it. Xbox codes skip the letters that look like numbers, so a typed 0 for an O is the usual mistake.
Paste into the single field. Dashes are added for you. Microsoft checks the code and shows you what it is worth and which region it belongs to before anything is applied.
You should see the exact value from your Keeoto listing and your account region. If the region does not match, stop here and open an issue on the order. Nothing has been used yet.