I'm a mobile application developer with 7 years of experience, currently unemployed, aspiring to pivot into a back-end development position. I do fiddle and experiment with some back-end development stacks on the side, but I believe the lack of professional experience might turn away most recruiters.
Given the situation,
Do you think I have to resort to restart my career from an entry-level position?
That actually the most important question. We cannot answer that for you, because we do not know in detail what you know.
However, consider this extreme example: you are the greatest guru in mobile applications. And you are sick of using computers, and you decide to become a shoes-maker. What chances will you have to perform as the greatest guru in shoes-making, from day one?
Bottom line: you might need to accept a lower "rank" for a while, until you get up-to-speed with your new job. Good luck. And until you get that dream job, keep improving your skills, so you can sell yourself better during the interviews. The company might accept to give you a high rank for your psychological comfort, but they might be ready to pay you only according to your skills - which is expected.
Do you have an advice on how I should prepare myself to suit the position?
Pick a back-end language and database and start learning from tutorials and blogs. Find some open source projects to contribute to.
Not sure what language you've done, but some back-end technologied may be easier to pick up depending - for example, experience with javascript would lend itself to working with node. Other language experience may point to PHP - if you do this, maybe pickup Symfony or Laravel as a framework - they're both in strong demand and pay well.
Do you think I have to resort to restart my career from an entry-level position?
Probably not a complete restart, especially if you can create or contribute to a couple of projects. You've already got some developer experience and skills. But you might have to take a short step back, first. It's not a great time right now, but if you can get to meetups and start networking, you might have an easier time than applying for positions.
A back-end developer who has some experience in the front-end is highly desirable for employers, even if you're going into a role that is 100% back-end.
IMHO, it wold be a smoother transition for you to move to full-stack developer
Look this post up: Don`t know if link posting is allowed, if not remove it please https://blog.udacity.com/2014/12/front-end-vs-back-end-vs-full-stack-web-developers.html
Choose the back-end tool/ framework and get acquainted with it. There is so much information on-line these days to learn your chosen path.
Getting certified in that chosen tool wold help your transition Lack of experience may be offset by the certification in the areas where you feel less comfortable
