Sometimes payments to a sellers account aren't released by Paypal immediately after an order is accepted. There can be several reasons for this. 

One of them is caused by the shipping information feature within the Paypal transaction:

Since Paypal introduced their marketplace system it has become possible for sellers to provide the shipping information to the transactions in their Paypal account. 

It's NOT recommended to use this feature as it will cause a delay in releasing the payment. 

When an order is accepted in our system we send Paypal a trigger to release a payment, but when there's tracking info provided within Paypal our triggers won't get processed immediately. Paypal waits with the release after they checked the delivery and this may take one till several weeks.

If the shipping info was provided to the transaction there are a few ways to speed up the process, see some of their help files on this subject:

In a case of a dispute PayPal will request the shipping information at a later stage. It is useful information to have but to speed up the payout from PayPal we advise not to supply the information upfront.

There also can be other reasons Paypal is blocking the payment. Please see the Paypal documentation about this subject: