What kind of editing do you need?
Work down these in order. Stop at the first one where the answer is no. That's the stage you're at, and paying for a later stage before you've cleared it's how writers waste money.
Is it finished?
Not polished, but finished. Beginning, middle, end, nothing marked "[fix this later]".
If no: you don't need an editor yet. You may want a manuscript assessment or a beta reader, a shorter, cheaper read that tells you whether the idea is working before you finish building it.
Are you confident the structure works?
Does it start in the right place, does the middle sag, does the ending earn itself. If you have a nagging feeling something is wrong but you can't name it, that counts as a no.
If no: you need developmental editing. It's the most expensive stage and the one that changes the book most. Everything after it's wasted money if the structure moves later.
Does the prose do what you want it to?
Read a page aloud. Does it sound like you, move at the right speed, and land where you meant it to?
If no: you need line editing. Sentence-level work on rhythm, clarity and voice. It's about effect, not correctness.
Is it consistent and correct throughout?
Same spellings, same names, timeline that holds, one style applied to numbers, dates and dialogue punctuation.
If no: you need copyediting. Grammar, consistency, style and accuracy, against a style guide.
Has it been through all of the above and you just want it clean?
Structure settled, prose worked, copyedit done, now laid out or formatted.
Then you need proofreading. The final pass. Typos, spacing, stray formatting.
The mistake almost everybody makes
Hiring a proofreader when you needed a developmental editor. It happens constantly, because proofreading is the cheapest line on the menu and "I just need someone to check it" feels like the modest, reasonable request.
What comes back is a clean copy of a manuscript with a structural problem. The typos are gone. The book still doesn't work, and you now have less money to fix it with.
A simple test. If the feedback you most fear is "this bit doesn't work," you need developmental editing. If it is "this sentence is clumsy," you need line editing. If it is "you spelled her name three ways," you need a copyedit.
Can one person do all of it?
Sometimes, and plenty of editors offer more than one. But be wary of a single quote covering everything in one pass, because these are genuinely different jobs done at different stages, and doing them simultaneously usually means one of them is being done lightly.
The honest version is either sequential passes, or an editor telling you plainly which stage they're working at.
What about beta readers?
Different thing, and often the right thing first. A beta reader is a reader, not a professional. They tell you where they got bored, confused, or stopped believing it. That's enormously useful, and it's a different job from editing.
Many writers get the most value from beta readers before a developmental edit, so they arrive with a sense of what's already wrong.