How to pay with mastercard at 7/11?

Hey, i have a couple of mastercards cards and lots of problems when trying to use them:)
I do know that they might not work everywhere but i have seven11 store (they accept mc) next to my location and sometimes there is a clever clerk at register that knows what to switch or select at register to make it accept my card. But most of the times the clerk present is clueless, they try to swipe the card without changing anything on register and of course the card gets rejected and they just say card cant be used. I come back after 1hour, new clerk is there, switch sth and does this without any problem. I once waited like 10mins in another shop when 1 clerk rushed to get another that knows how to accept mc cards.

My question is: is there some phrase in japanese that i can say to the clerk to help him change whatever it is on the register to use my card? I have debit not credit cards if that makes any difference.

But to my experience it is a bad idea to say that it is a debit card. At one shop lady at register asked is the card debit or credit and i said debit. She responded that it wont work and i have to use credit card. I insisted that it will work and asked her to give it a try buy she refused. I took the card and gave her another debit card saying this is credit, worked without any problems..:)

Even if you tell the clerk to "change something", if they don't know what to change, they don't know. This sort of thing is common in retail where turnover is high and new staff is not always trained in all the subtleties. When this happens to me I just let it slide and send a complaint to the relevant offices afterwards, suggesting they improve training of their staff. For 7-Eleven, it's here:

https://www.sej.co.jp/inquiry.html