I don’t know about online, but the best language learning system is to date someone who speaks that language, and not a word of English.
You must be able to think in Spanish and not simply translate from English. Learning sentence structure is the key. In your studies learn to write it. Reading is also key. Good luck.
That is how I learned Dutch back in the 60s. My firs serious girlfriend was a Dutch exchange student. She spoke perfect English but when she knew I was teaching myself some Hollands she quit speaking English with me.