I have no idea what an ATM card is, but if it's anything like a Debit Card then you should just be able to set up a PayPal account and attach that card to it.
You'll also need an email address you're not afraid to give out. I've created a "burner" email address that I use for all SqwarkDemon-related things.
If others also have a PayPal (most commissioners I find have PayPal) they can send the money to the email address you registered with.
Another alternative I've used in the past for my commissions is Ko-fi, but unless you're willing to pay for Ko-fi gold you can only accept payments in increments of $3.
However Ko-fi is apparently cracking down on lewd artists as of late so it's probably not the best site to use.
Paypal is also cracking down on lewd artists but it shouldn't affect you as long as you keep don't put "BIG ASS TITTY DRAW" or something strange in the payment description.
What I do whenever I accept commissions is read what the commissioner wants - lets say for example they want two characters hugging on a flat coloured background. The characters are their OCs.
For me I'd apply the basic polished and coloured lineart ($9) and extra character charge ($3) which comes to $12.
I'll tell them the price and ask if they're okay with it, and if they say yes we move on to drawing.
I've started asking for a 50% down-payment that covers at least the Lineart so they don't just take the drawings and run. (It hasn't happened to me yet but I wouldn't put it past people do that shit)Post too long. Click here to view the full text.