When your order is placed a temporary authorization is placed on your account by your bank or credit card issuer. We will request to capture that payment once your order ships.
Occasionally there is a gap between when the authorization is released and the payment is captured, or they may overlap - causing two payments to appear at the same time, one as a pending authorization and one as a true debit from your account. These variances are caused by differences in how individual card issuers process payments, and we are not able to impact the timing. Rest assured that the second transaction will disappear within a few business days.