tag = "hide" # If any line items have this tag, the gateway would be hidden
payment_gateways = ["Credit card", "BitPay"] # Any gateways in this array will be hidden
hide = false

Input.cart.line_items.each do |item|
  if item.variant.product.tags.include?(tag)
    hide = true
    break
  end
end

if hide == true
  Output.payment_gateways = Input.payment_gateways.delete_if do |payment_gateway|
    payment_gateways.include?(payment_gateway.name)
  end
end

Output.payment_gateways = Input.payment_gateways