Your contract, not your invoice, decides who owns the code
Paying for a website does not automatically transfer ownership of its code. What you actually own depends on the assignment or licence clause written into the contract, not the price you paid.
Many people assume that paying for a website or an application means owning everything that was built. That assumption is often wrong. The contract is where the truth sits, not the invoice.
What the contract actually decides
Ownership of source code is not automatic on payment. It depends on the licence or assignment clause written into the agreement. Some contracts transfer full copyright to you once the final invoice is paid. Others grant you a licence to use the software while the studio retains the underlying code. Neither approach is wrong, but they lead to very different outcomes, so you should know which one you signed.
Assignment clauses are the stronger form of transfer. They state that copyright in the code passes to you, usually on full payment. Once assigned, you can modify the code, move it to another developer or resell the product without asking permission. A licence works differently. It grants you rights to use the software for a stated purpose, but the studio keeps ownership. If the studio closes or the relationship ends badly, a licence can leave you without the rights you assumed you had.
Third party components complicate this further. Almost every project uses open source libraries, paid plugins or external services. Those components carry their own licences, and no contract between you and a studio can override them. A studio can only assign what it actually owns. Read the contract for a line that separates custom code from third party code, because that line tells you what you are actually acquiring.
Ownership is not what you paid. It is what the contract says you bought.
Why this matters at a fixed price
A fixed price project can create a false sense that everything is settled once the invoice is paid. Price and ownership are separate questions. You could pay a fixed price and still receive only a licence, if that is what the contract states. Before signing, ask directly whether the agreement assigns copyright or grants a licence. Ask what happens to the code if you want to change developers later. Ask whether design files, credentials and configuration are included in the handover, since source code alone is not always the whole product.
When you engage a studio at a fixed price, ask for the ownership clause to be written in plain terms before work begins. A short paragraph in a contract can be read in a minute, and it decides who controls your software long after the project ends. Do not let a clear price stand in for a clear clause. They are answering different questions, and only one of them tells you who owns the code.
If you are reviewing a contract from another studio, look for the ownership clause before you look at anything else. It matters more than the delivery date, and far more than the invoice total.