I seem to be having constant issues with customers  messaging me asking for a combined invoice -  but the items are not in my awaiting payment section - so I can’t send them a combined invoice? 

I message them asking to buy the items but don’t pay - but maybe I am not wording it right - as I usually get a few messages then the buyers give up 

I don’t require immediate payment on my

items 

I dont understand why some customers are able to buy items without paying & I can send them a revised invoice - but others seem unable to?

in my settings I have clicked the allow combined shipping button 

theory - do people need to use a computer to do this? 

does anyone have some clear instructions I can send  to buyers ? 

any help would be greatly appreciated as I seem to be losing sales every week -because some people are unable to buy items without paying 

many thanks in advance