Start here
I get this question by email most weeks. Here's the answer I actually send.
First, one question: can you read music?
Nothing extreme. Do you know the note names in treble and bass clef, and do you have some theory?
If no, start with The Staff Speaks. It's the bridge, and it builds notation and note-hearing from zero. Come back here after.
If yes, start with Flawless Ear Training.
The path
Start with Flawless Ear Training. The first week is free, so you find out whether it works on you before you spend anything. It's going to feel simple at first, but it's fixing old workarounds and habits that prevent you from audiating, and from knowing what you're audiating.
After about a month, I'd suggest adding the Composing Hour if you like my teaching style. The two courses work on different things. Flawless fixes your ability to understand what you hear. The Composing Hour trains you to create and shape music in your mind. Run them alongside each other.
That's basically it. Those two things combined last at least one year. One exception. If you can already dictate what you hear, you may not need more ear training. Start with the Composing Hour by itself.
No card to enter and nothing to cancel.
After that
If you finish the training and want a more theoretical background, there is Counterpoint for Composers and Form and Analysis. Though I recommend you work on audiation first.
Still not sure where you fit? Book a call or write to me. Either way, I'll ask you that same question about reading music and tell you where to start. I read every one.