It seems that some Uni requires Pre-Payment, e.g. St Andrew for unconditional offer or conditional offer when the conditions has been met. From their website
"Pre-payments
If you are an applicant who meets the following criteria, you are required to pay a pre-payment fee of £2,000 GBP against your first year’s tuition fee:
You have applied to an undergraduate programme.
You have a fees status of ‘Overseas’ in your offer letter.
For applicants who require a Student visa, the total amount paid to date including any pre-payment made will be displayed on your Confirmation of Acceptance for Studies (CAS), where appropriate.
Conditional offer
If you firmly accept a conditional offer, you are only required to make a pre-payment once you have met your stated conditions.
Please do not make a pre-payment whilst you are holding a conditional offer.
All the conditions stated in your offer must be satisfied before your admission can be finalised.
Once you have accepted your conditional offer and met your stated conditions, you are required to make a pre-payment within four weeks.
If you are holding a conditional offer through UCAS you are required to accept your Unconditional offer, before making your pre-payment.
Unconditional offer
If you firmly accept an unconditional offer, you are required to make a pre-payment upon acceptance.
A pre-payment must be made within four weeks of you accepting your Unconditional offer.
If you applied through either the Direct application or Common Application form and received an offer by 9 March 2023, you are required to make a pre-payment within 4 weeks of acceptance and no later than 5 May 2023.
If you applied through UCAS, please check the UCAS Hub or the UCAS website for the response deadlines that apply to you.
If a pre-payment remains unpaid, this will be taken as an indication that you no longer wish to take up the offer of a place at St Andrews.
Insurance choice
If you accept a conditional or an unconditional offer as your insurance choice through UCAS, you are not expected to make a pre-payment.
Pre-payments are required only if your status changes from ‘insurance’ to ‘unconditional firm’."
I think whether it is required to make a deposit or pre-payment depends and it should have been written in the Uni website.