1. Go here: https://etherscan.io/address/0x28cb7e841ee97947a86B06fA4090C8451f64c0be#writeContract
2. Hit "Connect to Web 3" link and connect to Metamask
3. Go to where it says "approve" and paste in: 0xC150EADe946079033c3B840bD7E81CDD5354E467
4. Under approve it says "amount" paste in: 40000000000000000000000000
5. Hit the blue "Write" button and accept the resulting TX in Metamask
6. Go back to https://yflink.io/#/staking and go to the Governance pool
7. Input the amount you wish to stake and hit "stake"
8. Accept the resulting TX in Metamask
9. Done! Now you can vote
Make sure you have more than 0.1 YFL in your wallet for voting or putting a proposal on-chain.
This is most likely because you have voted on a proposal. You need to wait three days after you've voted.