Gas and electricity regulator, Ofgem, has said that Tonik Energy has failed so approximately 130,000 households across Britain will need a new energy supplier.
Tonik Energy was identified as a supplier that had not paid money that they owed to Ofgem, thought to be £8.8m.
For now, customers are advised to sit tight - rather than trying to switch now - and Ofgem will appoint a new supplier to take over their accounts in a few weeks.
If customers do not like their new energy supplier, they will be able to change to another afterwards.
Will Owen, energy expert at Uswitch.com, said 'Many energy companies, particularly the smaller challenger brands, operate on thin profit margins.
'The Covid-19 lockdown has also resulted in many customers delaying or missing payments, leaving some suppliers without the cashflow to keep going day-to-day.
'Tonik Energy customers should wait until they know the final details of the new energy company selected by Ofgem, and the tariff that they will be offered, before they try to switch to another provider.
'While they're waiting for this to happen, we would urge Tonik Energy customers to note down their meter reading now, and again when they are contacted by the new supplier, so they can ensure their bills are accurate.'
Ofgem director of retail Philippa Pickford said: 'Tonik Energy customers do not need to worry, as under our safety net we'll make sure your energy supplies are secure and domestic customers' credit balances are protected.
'Ofgem will now choose a new supplier for you and whilst we are doing this our advice is to 'sit tight' and don't switch. You can rely on your energy supply as normal.
'We will update you when we have chosen a new supplier, who will then get in touch about your new tariff.'
On its website, Tonik said: 'Tonik Energy… is ceasing to trade. Ofgem, the energy regulator, is appointing a new supplier for its customers.
'Customers need not worry, their supplies are secure and domestic credit balances are protected.'