The option to hold Customer invoices is available from the ...More Options menu of an invoice. An 'On Hold' invoice cannot be posted as part of a bulk post operation.

From the invoice, go to ...More Options in the toolbar, and then select Hold.

The invoice will display the status of 'On Hold' in the toolbar.

When users go to post the invoice, they will be now be advised that the invoice is on hold and asked if they still wish to post it.

Put all invoices on hold by default

You can choose to ensure all invoices are placed on hold by default when saved. Go to Settings > Customer Invoice and Quote Settings. Switch on the button next to 'Put invoices on hold when saving'. Then select Save.

Bulk hold / remove hold of invoices

On the list view of invoices, you can hold or release the hold on invoices as a bulk action.  

Select the invoices in the list individually or select all, using the hold status drop down choose to place on hold or remove from hold.  This will ignore all invoices in the wrong state and those unable to be held e.g. those being picked.

The confirmation dialog will indicate the number of invoices that have been selected vs the number you can hold or unhold.