Around 4million households will not get the £400 energy bill discount automatically - and will need to take action to get it.
Today, the Government revealed more details about how it will run the Energy Bill Support Scheme.
This cash was announced in May, and homes in England, Scotland and Wales will get £400 off their energy bills as part of plans to tackle the cost of living crisis.
Most homes will get the discount applied automatically.
But if you have a pre-payment meter then you will be given vouchers to cash in instead.
Energy minister Greg Hands said: "I encourage families across the country to engage with these plans and particularly those customers on traditional prepayment meters who need to take action."
There are around 4million home with prepayment meters, according to energy regulator Ofgem.
If you have a smart prepayment meter then you don't have to do anything.
These customers will get the money credited directly to their meters.
This will happen in six instalments from October.
Customers get a £66 credit in October and November, then a £67 credit from December 2022 to March 2023.
But if you have an older, 'dumb' prepayment meter, you will get vouchers instead.
These will be handed out through text message, email or post.
People on prepayment meters can then cash these in at wherever they normally top up their energy, such as a PayPoint or Post Office.
Caroline Abrahams, charity director at Age UK, said: "Traditional prepayment meter users will have to rely on top-up vouchers, delivered via text, email and post, to access the scheme.
"We know from past experience, this will present significant barriers to many vulnerable older households.
"We encourage prepayment meter users to check their post over the autumn and winter for letters from their supplier as these may contain crucial top-up vouchers which will help you with your heating bill."
There is also uncertainty about how people with no energy meter will get the £400 energy bill discounts.
Many people, such as those living in park homes, pay a fee for energy to their landlord, who owns the meter itself.
That led to concerns that they would not get the £400 discount as it would go to the bill payer - their landlord.
But the Government has announced more cash will be available for people in this category.
The Government said: "As part of this package, we are confirming today that further funding will be available to provide equivalent support of £400 for energy bills for the 1% of households who will not be reached through the Energy Bills Support Scheme.
"This includes those who do not have a domestic electricity meter or a direct relationship with an energy supplier, such as park home residents."
Private renters with their own meter will get the £400 discount.
Tenants who buy electricity and gas from their landlords should get the payments from their landlord.
Renters who get energy bundled in with their rent should speak to their landlord about getting some money back.
If you rent somewhere with a commercial energy meter - as some housing association tenants do - the Government will announce more plans in the Autumn to help.
If you pay by direct debit
Direct debit customers will get the discount automatically as a deduction to their monthly bill.
Alternatively they will get a refund to their bank account for six months from October 2022.
If you pay by credit or payment cards
Standard credit customers and payment card customers will get the discount as a credit to their accounts.
This will happen in the first week of each of the six months the discount scheme is running.