Thanks but tried to sign the transaction with my bitcoin address and it wouldn't even sign it so back to the drawing board

Yes coinb.in so far I have have tried to sign the transaction hex with my electrum key then when I try to broadcast i get that error. That's as far is I have got unfortunately

Thanks for the reply it's a multisig and already has one signature so just requires me to sign and broadcast. As I previously said I'm out my depth here but am sure there is no scams happening. Could you point me in the right direction here?

I have received a redeem script and transaction to sign on order to get a refund. When trying to broadcast the signed transaction I get the following error.. any help would be greatly appreciated as I'm lost with this..

mandatory-script-verify-flag-failed (Operation not valid with the current stack size) (code 16)