Does investing in freelance sites guarantee orders?

So I'm a high school student in Italy, this summer I got a paid internship at a medium-sized tech company (by local standards), mainly working on app development with flutter and PHP.

However, I would like to be able to continue somewhat working when school starts as well, however not being employed at a company but preferably doing freelance projects. I have tried many of those sites before: Fiverr, Design crowd, Freelancer, and never had any success. Will investing some money into these sites realistically change anything? (I have about 400 euros), is this a worthwhile investment? And will I have to keep dumping money into these to keep getting anything out?