For as long as I know, Opera is a secure browser to manage payments. There may be some support issues that you might be encountering. Besides, it can be an issue with your specific version of the browser. You can ask any friend near you to help you check with it if they could handle payments with Opera. Otherwise, you have to switch to some other payment mode or app.
I believe, if users are facing such issues, Opera really needs some serious check on quality assurance. Rest, let me know if making updates or changing device help you process payments.