A shopping centre has lost 40% of its revenue since RingGo-only payments were introduced at its car park by the council, say devastated bosses.
Meanwhile, customers still using De Bradelei Wharf in Dover say they are avoiding the new system by paying with coins or card at spaces outside the complex.
The system was introduced in the spring by landowners the Port of Dover and Dover District Council, which manages the car park.
There are now no parking payment machines at the site - so the only way of paying for your space is by using the RingGo app or making a telephone call.
But De Bradelei Wharf manager Sally-Anne Vokes says many of the centre's customers are older people who don't have smartphones.
Loyal regulars who have been coming to the shops for years now say they won't be returning.
"RingGo has lost us a lot of custom - we have lost 40% of our revenue since it came in," Ms Vokes said.
"A lot of our customers are more elderly people, a lot without smartphones.
"We've had some say to us: 'We're really sorry but we won't be back because we cannot use that car park.'
"It's devastating to us. These are customers we've had for years. Some people think we have done this - but it's not us."
Gloria Coultan, co-director of the Boardwalk Café franchise within the centre, told KentOnline they have "lost most of our regulars".
"These are elderly people and they don't have access to smartphones so they have no way of paying," she said.
"They drive down here and when they see there is no coin system they drive back out.
"We have lots of complaints from people saying they are unable to use the shopping outlet any more because of the parking."
RingGo requires payment through a smartphone, either by using an app or making a voice telephone call.
Payment can be made by drivers giving their credit or debit card details.
De Bradelei Wharf has no payment machines now, therefore also cutting out the chance of using the contactless method with your card.
Customer Sheila Cope, 84, has a smartphone but doesn't use it for financial transactions because, like some others, she isn't convinced that they are secure enough.
Three weeks ago she drove to the centre with her daughter who had to step in to go through the process of paying with the new system.
Mrs Cope said: "If she hadn't been there and I had been on my own I would have just had to drive away.
"I shall not be attempting to use this car park again.
"At least there are alternatives such as the district council spaces on the seafront.
"But I think this RingGo system will eventually creep across other car parks."
Mrs Cope understands that many find RingGo convenient but believes people should be given a choice of method, including the option of paying by cash.
KentOnline met another customer, Roger Gambrill, who was at De Bradelei Wharf having avoided its car park by leaving his car at Dover seafront and paying with coins.
He said: "I have not got the app for RingGo. A lot of people of a certain age don't carry smartphones."
Another shopper, Ronald Denton, was there with his wife Lesley and also used a pay-and-display car park nearby.
He said: "We've been coming here for years. We don't pay by card or phone - we don't have that kind of technology. We pay cash and you can't do it here. I don't get on with the technology."
Mrs Denton said: "When we were parking there were two ladies who arrived near us and they said they will not use this car park."
RingGo is an increasingly-used system, with other local authorities adopting it.
Canterbury City Council has rolled it out at a number of its spaces.
Some elderly people in that district have also argued it cuts out people who don't have smartphones.
De Bradelei Wharf is on Port of Dover land but Dover District Council (DDC) took over managing the centre's car park, and most others in the harbour area, in April.
The council's parking spaces elsewhere have RingGo but also still an option to use coins.
A DDC spokesman said: "We manage the De Bradelei Wharf car park on behalf of the Port of Dover, and are guided by their decisions on matters such as available payment methods.
"We do not currently have RingGo-only systems in DDC-owned car parks. However, this could be something we may consider in the future.
"We are also looking to consult on proposals for RingGo-only for on-street parking around Coombe Valley Road in Dover if no permit is held."
A Port of Dover spokesperson said: "All Port of Dover car parks are managed by Dover District Council, who took over the running and enforcement of off-street pay and display parking back in April of this year.
"This excludes parking at the Eastern Docks ferry terminal or cruise parking at the Western Docks.
"This delivered a uniform approach to waterfront parking provision, with DDC already being responsible for on-street parking enforcement along Marine Parade.
"The decision to move to the RingGo payment system was made alongside DDC during the handover of responsibility for management of the car parks."
So how hard is paying with RingGo? KentOnline reporter Sam Lennon, 58, gave it a go...
I figured that the white heat of technology would catch up with me sooner or later, so I decided to learn how to use RingGo.
The system is spreading, with other car parks also only accepting this form of payment. I'm part of the generation that carries fistfuls of coins in my pockets ready to pay for parking whenever needed.
Until lately I had only heard of Ringo, the drummer of The Beatles.
But one day I might be in a dead end with a car park only accepting this new system.
It's happened to me a couple of times in Folkestone and Ashford when the coin machine was temporarily out of order and RingGo was the only way. I tried to pay by telephoning the automated system but found myself confused by what the space age-voices were saying. I got so angry and frustrated I ended up shouting at them.
Doesn't matter, robots don't take things personally.
Friends told me the app was best and it was easy to use once you got the hang of it.
My journey of learning began in June when a colleague 33 years younger than me guided me on how to download the app.
"There is no question that this system shuts out anyone without a smartphone..."
Somehow I was able to get away with still paying analogue style, with cash, but I decided to have a serious try when I knew I was going to research this story.
The night before I went to De Bradelei Wharf, I read up on the internet how RingGo worked.
Using my app I was able to follow the instructions to register my open credit card details so it could take payment, plus my mobile phone number for messages and alerts.
Crunch time came yesterday morning (Tuesday) when I arrived at the centre and it took time to get used to seeing no payment machines.
In that first ever attempt I needed my hand held, so I asked the first person I saw, a Port of Dover employee, to guide me.
It first meant writing the location number for the car park, which is clearly displayed.
The rest was like filling in a paper form, except this time by smartphone, keying in your registration number and saying how long you want to stay.
Job done, and a text message was sent to me confirming parking times and how much it cost - £2 for an hour.
"The secret is never be embarrassed about asking someone nearby to help you..."
The payment was taken straight from my credit card, which of course I have previously registered.
It didn't seem too difficult and I think it will take a little more practice until I completely grasp this.
There is no question that this system shuts out anyone without a smartphone and for those who do have one it can seem bewildering and nerve-wracking learning it for the first time.
So, above all, the secret is never be embarrassed about asking someone nearby to help you.
You never invented this system - so you're not supposed to know how it works until you are taught.