You know, in the Android Electrum Send tab there is a button (diskette) which is a Save transaction button indeed, I think.
When I press it Electrum says 'invoice saved'. But where is it saved , no idea.
I  thought it was a sort of the Desktop's Export button (which can be used to save and pass transactions from Desktop watch-only wallets.
Well , actually I see there's NO clear and simple way to use Android Electrum watch-only wallet. Now I have to copy-paste BTC address , amount from destination to my Desktop's watch-only wallet. Instead of using an instant and so pleasant scanning QR code method