4. Following your instructions I could actually get the destination address to appear in the field where you usually would get it by the way of the drop down menu, but as I've clicked send I've got the mistake: "Impossible to send the payment: precommit callback failed: [a string of text]: conflicting spend proof in inner unit [a string of text]"
Sounds like the "bytes" you have are possibly not valid... due to being used in another transaction. Not sure if it's referring to the "normal" bytes or the "blackbytes".
So, do you know if you are trying to send blackbytes that are no longer available? Did you at some point restore from an old backup or have the same wallet (same seed) running on more than one device or anything that you think could have somehow corrupted one or both the wallets?
In fact I have made a little mess, after your comment I've realized it, the wallet with the blackbytes to be transferred I have just discovered was an old FULL node wallet which I've opened with a light wallet app just by renaming the data folders - it's quite logic it wouldn't work I guess. To get it work I suppose I should restore an old backup. Well, this would be good news, it means no bugs in Byteball wallet and some bugs just in my mind

still dont works after restore frome backup i buy some gbb and that whats sow up
Uncaught exception: Error: Error: SQLITE_ERROR: no such index: outputsIsSerial SELECT unit, message_index, sequence FROM outputs INDEXED BY outputsIsSerial JOIN units USING(unit) WHERE outputs.is_serial IS NULL AND units.is_stable=1 AND is_spent=0