Hi. I am Nikola. I have checked on your requirements. Which platform do you want, I am unclear. But "payment page( iFrame ) doesn't show sometimes." ... I think this is web.
I am a professional Web developer and I have experience in Mobile app integration too.
I have developed a WordPress theme and plugin based on jQuery, CSS3, Bootstrap and HTML5 from 2015. Now I am using CSS4 and Bootstrap 4 for Mobile-friendly sites, and am using woocommerce plugin for WP.
Other than that I am using node.js, Angular JS, MERAN Stack, CI, Larabel and etc.
Now, I am developing Magento for eCommerce site.
If you award me your project, I can show my trust and professional work.
Let's meet from the chatting.
Thanks.
[login to view URL]