The short answer
Credit cards, plus ACH bank transfer for any payment of $1,000 or more. HighLevel's billing FAQ says it does not accept PayPal or checks. ACH payments take 3 to 10 business days to process, and a card remains available for every amount. The subscription and the usage wallet are billed separately, and wallet credits cannot pay the monthly or yearly plan fee.
Paying for your plan
Signup asks for a card, and the free trial page says the card on file is charged when the trial ends unless you cancel. ACH is mainly useful for large payments such as an annual Unlimited plan at $2,970 or Agency Pro at $4,970. You update the card under Agency Settings, then Billing. If a subscription payment fails, HighLevel's billing FAQ says the agency keeps account access for 21 days from the failed payment date, which gives you time to fix the card before anything is cut off.
How the usage wallet is paid
Texts, calls, email, phone numbers and pay-per-use AI draw from a prepaid agency wallet. When the balance drops below its minimum, HighLevel charges the card on file to refill it, and the Terms say a negative balance is also charged to that card automatically. Because wallet credits cannot pay the subscription and both depend on the same card, one declined card can affect your plan and your messaging at once. Keep a card with enough room that a busy month of client texting does not cause a decline.
Payment methods your own customers can use
Taking payments from your customers is a separate matter. HighLevel's invoices, order forms and other payment tools connect to outside processors, and its help center names Stripe, PayPal, Square, NMI, Authorize.net and Razorpay, with PayPal supported on both order forms and invoices. So while HighLevel will not take PayPal for its own subscription, a business on HighLevel can still let customers pay through PayPal, with that processor's fees applying to each sale.
More answers in HighLevel questions. For costs, see GoHighLevel pricing or run the cost calculator.