This could be due to many reasons:
- Insufficient balance: Make sure you have enough CSPR to pay for gas fees (around 3CSPR to 5CSPR)
- Casper Signer: If you are using Casper Signer, make sure the extension is active and is working. Try refreshing the page and/or restarting the browser and trying again.
The smart contract has not been approved to spend your tokens. Make sure you approve the smart contract first.
You need to wait for the transaction to be picked up by the nodes and included in the blockchain. This usually takes around 30 secs.