You have to pay your tax bill by 31 January each year for the tax year ending 5 April beforehand. So you have 9 months to settle up.
There are a few ways to pay to your self-assessment which are explained on the Gov website. Paying with Coconut there are two main options:
1. Pay by Card
You can pay your tax bill online here.
2. Pay by Bank Transfer
You can pay by bank transfer from your business account to HMRC. The account details can be found on HMRC's website here.
You'll need to include your 10 digit Unique Taxpayer Reference (UTR) followed by the letter "K". You can find your UTR on your paper statements from HMRC and also through your online account if you have one set up.
3. Other ways to pay
There are a few other ways to pay too:
If you can't afford to pay your tax bill in time, it's worth checking in with their Business Payment Support Service. They are sometimes able to arrange payment plans if you're unable to pay.