Hello,
You'd need to arrange this within your website itself. PayPal unfortunately does not let you 'pause' payments.
With regards to your order system; you may want to start using PayPal Authorization & Capture. With Authorization & Capture, a buyer would authorize a transaction for a certain amount, and within 3 or 29 days*, you can 'capture' the funds and the transaction will be finalized.
To start using this with a PayPal payment button, simply add the following extra line of code to your existing PayPal button(s):
<input type="hidden" name="paymentaction" value="authorization">
Once a buyer has authorized a payment, you'll see a 'Capture' button in the PayPal transaction overview of your PayPal account.
* An authorization is valid for 29 days, but we only guarantee that you can capture the funds for 3 days. Beyond 3 days, the transaction may or may not go through depending on the buyer's situation.
For more information on PayPal Authorization & Capture, please see https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_admin_authcapture
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