Setting the Approval Flag to True

If you define an approval process for a specific object and want the process to be initiated on click of a button, go to Create > Objects > [Object Name] Quote > [Field Name]Configure Products(Field), edit the formula field and set useAdvancedApproval=true.

For example:

IF ( LEN( Apttus_QPConfig__PriceListId__c ) > 0 , \
HYPERLINK("/apex/Apttus_QPConfig__ProposalConfiguration?id=" &Id&"&useAdvancedApproval=true&useDealOptimizer=true", \
IMAGE("/resource/Apttus_QPConfig__Button_Configure", "Configure Products"),"_self"), NULL)