If there is a list of annoying false things technology people believe about business, this notion that bill rates track technical ability would have to be near the top of it.
Your rate has almost nothing to do with how good a programmer you are. Sorry, excellent programmers who've had a hard time getting consultancies launched.
Your bill rate roughly† tracks how much value you provide to your client. "Value" is complicated and situational. For programming work, for most clients, extreme technical excellence is of marginal value. Clients that engage third party developers tend to see software as a cost center and/or are simply trying to solve a business problem. They care about how quickly that problem can be workably solved, and (please take notes:) how predictable the costs are.
You can be thoroughly mediocre at programming and an excellent business value, if your mediocre code solves business problems people will allocate budget for and if you can deliver it predictably. If you can deliver predictably and fast, you can ship bog-standard PHP code and charge integer multiples of what a much better developer might implement in Rust or Haskell.
The market tends to pay a premium for problem domain specialization, and less of a premium for elite skill.
None of this much matters for someone just getting their feet wet trying to get their first couple clients. Do whatever gets you started. But get out of the habit of convincing yourself that you have to qualify somehow to charge more money. Even the consultants who are constantly telling people to raise their rates are also not charging enough. I'm a varsity member of team "raise your rates" and I thought we were undercharging 4 years ago. Since then, FTE rates have gone through the ceiling and our rates have not scaled with them. It is very unlikely that any consultant chatting about consulting on HN is charging their real market rate.
I have one bit of bad news for you: if you want to make a career out of being a contractor or consultant, you need to get off freelancing sites ASAP. It's fine to get started there, but you're not developing your practice in any meaningful way as long as you're using them; you're just getting better at slinging code (which doesn't earn you better rates!), while radically undercharging clients. Getting off freelancing sites is rough, because freelancing sites tend to provide a comparatively stable revenue stream, and real consulting revenue is lumpy. If you've never experienced "lumpy" before: it's (a) terrifying and (b) really easy to screw up, by assuming you're flush with cash when really you've effectively just been pre-paid for the next N quarters.
Some people reasonably don't want to work under lumpy consulting conditions. Better you figure that problem out for yourself early rather than wasting your time pretending, or, worse, forgoing a fuckload of income by chaining yourself to freelance sites.
† Roughly because most serious clients allocate a budget that establishes a range of what they're willing to pay to solve a problem, and an invisible component of that budget is how much work they're willing to put in to sourcing a contractor --- the first credible contractor they talk to might win the deal, meaning there's no competition to aid price discovery. Corollary: one way to "provide value" and charge a premium is to be easy to source. Something that people who build consulting firms, the kind with lots of consultants, learn quickly: clients put a premium on firms that are always available.