To be honest, I wouldn't recommend using the online form at all for FLR(M). It's new, glitchy and has different questions to the paper form.
I would just print out the paper form and fill it in by hand. We know exactly how you should fill out the paper form and can see it when giving advice... whereas I have no clue what the online form looks like!
Using the paper form, if you're applying by post, you'll need to include payment details with your documents. If you apply in person (using the paper form), you pay for the visa when you book your appointment.