I never made a sale on my Shopify store

I run an eyeglasses store here in Brazil. Before, I used to leave tons of models and lenses all open so the customer could pick their frames and lenses. I realized that the customer journey to buy prescription glasses was super complex and usually depended on someone to convince them, since buying prescription glasses online is kinda tricky, and I see people need a lot of proof before making that purchase—it’s not usually an impulse buy. ​So, I tried a strategy change: selling a simpler product, which is glasses with blue light filter lenses (non-prescription). I see other people running a lot of ads on Facebook from the library, but my budget is pretty small, and I'd like to have some kind of success. I’ve made several changes to my collection and product pages, but I haven't gotten anything more than a few 'add to carts.' ​What could I be doing wrong? Do you really need a huge budget to test audiences?" ​My website is https://www.oculosstore.com.br