If the person whom you believe owes you money does not live in England & Wales, it complicates things. Even if they live in Scotland or Northern Ireland, both of these parts of the country have separate court systems with slightly different laws. It is what is known as being outside the jurisdiction of the courts of England & Wales.
You need to decide where it is best to lodge your small claim — in your jurisdiction, or theirs. The reason for this is partly because you are required to ‘serve’ the defendant with notice that you are suing them. This is a legal requirement in the courts of England & Wales. If the defendant is a company with an office or base in England & Wales, it may be that you can serve proceedings via their offices in this jurisdiction. If they live abroad, you may need to ask the court’s permission to serve notice that you are suing them.
If you want to serve a claim against someone living in the European Union, this process is more complicated since the UK left the EU. If they live outside the EU, it may be considerably more complicated due to the laws of the foreign jurisdiction. You may want to seek legal advice if the person or company you are looking to sue is outside of England & Wales.