Transfer/deposit ether on contract fails

I am trying to deposit Ether on a smart contract. Looking at the documentation
my approach first looked like this:

// SPDX-License-Identifier: MIT
pragma solidity ^0.0.8;

contract SendEther {

    function deposit(uint256 amount) public payable {
        require(msg.value == amount);
    }
}

However, that failed with the following error message:

[vm]

from: 0x5c6…21678

to: SendEther.deposit(uint256) 0xe63…4ddf5

value: 0 wei

data: 0xb6b…03039

logs: 0

hash: 0x50c…acc83

status false Transaction mined but execution failed

transaction
hash 0x50cb8aab1042aef79e8bf285346213a1edfa106b2a7421ee159da82b693acc83

from 0x5c6B0f7Bf3E7ce046039Bd8FABdfD3f9F5021678

to SendEther.deposit(uint256)
0xe63D12C600b87F5da3C32C7cB3C1b1A84944ddf5 gas 3000000 gas transaction
cost 21614 gas execution cost 21614 gas input 0xb6b…03039 decoded
input { "uint256 amount": "12345" } decoded output {} logs [] val 0
wei

transact to SendEther.deposit errored: VM error: revert.

revert The transaction has been reverted to the initial state.

Note: The called function should be payable if you send value and the
value you send should be less than your current balance.

Debug the transaction to get more information.

Then I tried to use the transfer or call method to send Ether.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SendEther {

    receive() external payable {}

    function sendViaTransfer(address payable to, uint256 amount) public payable {
        to.transfer(amount);
    }
}

Which resulted in this error:

[vm]

from: 0x147…C160C

to: SendEther.sendViaTransfer(address,uint256) 0x70c…a304B

value: 0 wei

data: 0xd27…004d2

logs: 0

hash: 0xc29…0cf23

status false Transaction mined but execution failed

transaction
hash 0xc296ba642bca2e19c304a9e28381b3b523fdb86a94fcbc19e14ad5847a20cf23

from 0x14723A09ACff6D2A60DcdF7aA4AFf308FDDC160C

to SendEther.sendViaTransfer(address,uint256)
0x70c001c84C723e3EfbF852D3e6AdaEb69A8a304B

gas 3000000 gas

transaction cost 29070 gas

execution cost 29070 gas

input 0xd27…004d2

decoded input {

"address to": "0x70c001c84C723e3EfbF852D3e6AdaEb69A8a304B",

"uint256 amount": "1234"

}

decoded output {}

logs []

val 0 wei

transact to SendEther.sendViaTransfer errored: VM error: revert.

revert The transaction has been reverted to the initial state.

Trying to use "call" or "send" results in the same error.

What am I doing wrong?