I’m a freelancer, and got my first paid Elixir gig through a consulting shop I often work through. I’d made quite a bit of noise about my enthusiasm for Elixir with them, and even organized a meetup in my city. So when there was a sudden need for an experienced developer to work in a client project, I was asked to help out. I was able to hit the ground running, no trouble, and charging my usual rate.
I suggest looking into networking as a way to help out with migration to professional elixir work. Attend (or organize) meetups, maybe give a talk or two, get to know other Elixir enthusiasts in the area. That way, when their company needs new developers, it’s very likely they’ll give you a call.
As for why they should pay you the senior developer rates even though you haven’t worked professionally with Elixir before? Elixir is only one part of the tech stack. Let’s take a web development project that is working with Elixir, Phoenix, PostgreSQL, Docker, Nginx, JavaScript ecosystem and so on. Of course, they also use ubiquitous technologies that are usually not even mentioned when looking for developers: HTTP, TCP/IP, DNS, HTML, CSS and so on. Odds are, if you’ve been working with web development before, you already have experience with a lot of that.
In addition, you have experience in aspects of work that are as important as programming skill itself, such as the ability to communicate clearly, clarify requirements, and confidence to push back and suggest alternatives when you can think of a better way. All this experience, both technological and “soft skills”, is worth a lot in terms of development speed and quality, and is therefore a good reason to pay you well. Lacking professional experience in some parts of the stack is not that important, especially when you have the personal enthusiasm to study and practice just those parts on your own. As developers, we have to learn new technologies for new projects all the time anyway.
For interviews, I believe it’s important to internalize the way of thinking I outlined above, and not sell yourself short. It’s easier to convince others of your value if you’re convinced of it yourself.