I've used PayPal for the longest time, and I think everyone I've commissioned has used it too, so it's a good bet for commissions. I just usually ask the commissioner for their email, then send a request for the said price, and they'll usually pay it (Sometimes PayPal takes like 2$ fee for the payment, which depends on the commissioner if they pay for it or not - you can require that as part of your ToS). Oh also it's important when you're requesting the payment, I've heard some descriptions can get you banned, namely NSFW subjects. So vague stuff like "Gaggosmies commission" or "Full body drawing" is usually the best.

Making Terms of Service is pretty important too, in case there's complicated customers. That's for if they keep changing the drawing subject or if they change details after or any of sorts. Also that's a good place to store what you're willing to draw and what are off limits.

PayPal works pretty well as a payment method in the online, since you can use it pretty much everywhere. I don't think a debit card is necessarily required, but after some threshold (I think gaining ~2k$/year) will require you to add the details.

Looking at your prices, you might wanna look into Ko-Fi, which is a service that connects to your PayPal. It's like a tipping service, and you could sell busts for 2 Ko-Fis (6$ - with PayPal fees off it's like 5$, whereas paying through PayPal entirely would cost about 7$ for the commissioner).

I’m not sure if this is the right place to ask, but are commissions still available by any chance?