Yup. You can't increase the fees on the transactions that you have already broadcasted. If you have the replace by fee option selected, you can create another transaction with a much higher fee to "replace" the current transaction that is in the mempool.

Sure. Child pay for parents allows for child transaction (the transaction you are creating) to help to incentivise the miners to get the whole chain of transaction confirmed. This method will work as long as the transaction has an output to an address that you control. This does include a hefty fee however, since you are also effectively creating a new transaction.

There are a couple of ways you can do this. This is how I'd do it in Electrum:

1) Replace by fee - In electrum there's the ability to go to "If fee is too low" or "Always" from Fee preferences in Tools. This would've then let you select 'Replacable' to allowed you to later on replace the fee of your existing transaction. Could you check if Mycelium allows this feature? I'm not sure since I haven't used that wallet. I believe I was able to do this in electrum by right clicking on the unconfirmed transaction -> selecting increase fee --> then setting a higher fee or using electrum's dynamic fee that was already set.

2) This is possible now if you're receiving the funds - Child-pays-for-parent  - In the 'History' section right click on the transaction that is unconfirmed and then selected Child pays for parent -> increase the fee this time to a suitable fee (calculate it from here: https://bitcoinfees.earn.com/) -> Sign and broadcast the transaction.

3) By using a transaction accelerator like confirmtx, viabtc's tx accelerator or antpools tx accelerator. I've accelerated your transaction on confirmtx and antpool's accelerator. It might get confirmed in upcoming blocks when they include your tx in their block that is mined. If you can't wait for this option to have your tx confirmed, follow option 2 if you're receiving the funds.

Edit: Updated post after confirmation.

So you've already created and broadcasted this transaction :https://blockchain.info/tx/3bf2e0fdd4a9ad01b83c679f83c247d019ecfa6f18c4fd075978b2c47075200a but it is unconfirmed due to low fees.

you do not need to create a file! simply open your Electrum, and from the menu select Tools > Load transaction > From text
and then just paste the raw unsigned transaction there.

i'm not sure why it is showing 'Status: Signed', that is really strange and it shouldn't do that.

but in any case Electrum will not recognize nor sign this raw unsigned transaction because your ScriptSig field is empty and Electrum needs to know which private key to use for signing the transaction.


use at your own risk.

{
    "final": false,
    "complete": false,
    "hex": "0100000001d45343bf472dcb8ca243daccf39b49399065e52bc310068641609cb48f24433c00000 00000ffffffff0240c7130d000000001976a914ed7de5536a51adb2ffa6a8550754b031d73fe19e 88ac1ef161000000000017a91461b10fa7361e7e62285a03532263790541f563d58700000000"
}

I'm a big fan of people wanting to learn
The "problem" is that it's easyer to create a raw, unsigned transaction if you're running a synced node (like i am doing), electrum is perfect for signing transactions, but not so good at doublespending unspent outputs that have already been spent.

If you want to learn the basics, you can download the sourcecode of coinb.in, i've actually written a small post on my blog on it's basic usage a long time ago: http://www.mocacinno.com/blog/create-sign-broadcast-transactions-using-coinb/
I wouldn't use coinb.in to sign the transaction tough (so you don't need to follow the complete article).

If you succeeded in creating a double spending tx using coinb.in, please post the unsigned transaction in this thread and i'll review it for you and give you some pointers on how to sign it using electrum

A big thanks to HCP for helping me get trough the many requests... Couldn't do this without a little help from time to time  

It looks like this is the only question left open at the moment:

I'll create a double spending transaction for you... The only thing i wanted to ask: could you tell me which output value i can take the extra fee from? You're funding 1Nejxrk4Y9Q2eQ6YTd3hMi46uSnnN4Ghbn and 3AbZaaKj4ZVomw4YKTTpraqQYbaesByTpJ, i'll have to reduce one of these outputs to leave room for a bigger fee... It's up to you to pick witch one.

Once you tell me where to take the fee from, i'll create an unsigned transaction, since you moved to electrum, you *should* be able to sign said transaction with your electrum wallet and broadcast it afterwards. It's been a while since i last did this, so i hope it still works, but i don't think it'll be a big problem

No. Double spending requires that you use the same inputs... If you just create a new transaction without knowing what you're doing, you could spend "different" coins and end up sending 2 payments! Best wait for mocacinno to help!

Since the receiver is an exchange, this pretty much rules out CPFP, the tx isn't opt-in RBF so that's out of the question to...
Multibit HD is no longer supported, if you move away from multibit HD to electrum (tutorial can be found here: https://multibit.org/blog/2017/07/26/multibit-shutdown.html), you SHOULD be able to follow my wizard on http://www.mocacinno.com/page/feechecker to create, sign and broadcast a transaction double spending the inputs of the unconfirmed transaction using electrum

Are you the sender or the receiver, and which kind of wallet software were you using?