Verify

Short answer: Three checks from your pilot home: email, Discord, then your DCS UCID. You cannot enter an OTS until all three are done.

1. Email. Click the confirmation link SFL emails you.
2. Discord. Paste your Discord User ID on your pilot home (the page shows how to copy it from Discord), join the SFL Discord, then confirm with the verify message.
3. DCS UCID. Choose Verify my DCS UCID and run the UCID-Verify Tool (see What does the UCID-Verify Tool do?).

Your pilot home shows each check as done or open, and it is where you pick up a step you have not finished.

Source: Your pilot home · Appendix B §B.2.3 (Appendix B tab)

Short answer: It is a small Windows tool from SFL that links the DCS account you fly with to your SFL registration. It takes about two minutes and runs once.

1. Update DCS first. New to DCS? Launch it once, sign in with your Eagle Dynamics account and reach the main menu.
2. On your pilot home, choose Verify my DCS UCID, then Get my code.
3. Download the verification tool, run it and type in the code. If Windows warns about an unrecognized app, choose More info, then Run anyway.
4. Leave it alone. It starts DCS, joins SFL's verification server for a moment, and closes DCS again. Being turned away by that server straight after joining is expected.
5. The page shows Verified. The tool closes DCS and tidies up on its own.

• Cannot run the tool? The page shows how to join by hand with your code instead.
• Not verified within a minute? Get a fresh code and try once more, or ask in #sfl-support on the SFL Discord.

The SFL Virtual Pilot Kit (VPK) is a different program; see Downloads and tools.

Source: Verify your DCS pilot ID · Appendix B §B.2.3 and §B.10 (Appendix B tab)

Short answer: The one you will practice and compete with. Your UCID is permanent to your Eagle Dynamics (or Steam) account, and once checked it is locked to your entry until finals.

• Whatever account DCS is signed in as when you run the tool is the one that gets linked. Sign in with the account you fly every SFL run on before you start.
• Reinstalling DCS does not change your UCID, but a second Eagle Dynamics or Steam account has a different one.
• Your DCS account is checked at verification and locked to your entry until finals. Run the tool again to re-verify only if SFL asks you to.

Source: Verify your DCS pilot ID · Appendix B §B.2.3 (Appendix B tab) · SFL Privacy Notice

Short answer: Sign in to your pilot home. It shows which check is still open, with a button to finish it.

• Discord: use Verify my Discord on your pilot home.
• Email: if the confirmation link did not work, reset your password. Completing the reset verifies your email address.
• DCS UCID: use Verify my DCS UCID, get a fresh code and run the tool again.

Source: Your pilot home · Appendix B §B.2.3 (Appendix B tab)