You can mark a transaction as RBF, but that does not mean that it is always possible to actually make an RBF transaction.
To do RBF in Electrum, you need a "change" output that is sufficiently large that you can take money from that output and use it as extra fees. If your transaction contained no "change" coming back to your wallet, you cannot RBF it in Electrum, because then you would be taking money from the amount you were trying to send... likewise, if the change amount was too small, then there would be no point trying to use it as it would either create "dust" and be rejected by a lot of nodes, or it wouldn't increase the fee enough to make a difference anyway.
To do RBF in Electrum, you need a "change" output that is sufficiently large that you can take money from that output and use it as extra fees. If your transaction contained no "change" coming back to your wallet, you cannot RBF it in Electrum, because then you would be taking money from the amount you were trying to send... likewise, if the change amount was too small, then there would be no point trying to use it as it would either create "dust" and be rejected by a lot of nodes, or it wouldn't increase the fee enough to make a difference anyway.
Yes, I have discovered this behavior, I wished Electrum wallet would have displayed the maximum amount you can bump a RBF transaction based on the output left prior broadcasting, for the moment I am really stuck because I have no room to increase the transaction fee.
