So you can do at max 100 callouts in a transaction.
As I can see you are Setting batch scope as 50. Database.executebatch(objTest, 50);
As you say, for each Account you will be making 12 Folder ie 12 Callouts.
So in each iteration of execute of Batch, you need 12(Folder) *50 (Account) = 600 callouts.
As we cannot do 600 Callouts in execute, you need to change the scope of your batch to the optimal value.
100(Callout)/12(Folder) = 8.3
that means your scope will be 8.
thus the fix will be:
AccountBoxFolderCreationBatch objTest = new AccountBoxFolderCreationBatch();
Database.executebatch(objTest, 8);
Edit: It looks like more than 1 callouts are used by Box API to create a folder. We have 2 options,do trial and error method or, try to find out how many callouts are taken by 1 account. We would try calling execute method to see a number of callouts made.
List<Account> AccList=[
select
Id,
Box_Folder_Id__c,
Financial_Accounts_Parent_Box_Folder_Id__c,
CLG_Opportunities_Parent_Box_Folder_Id__c,
Real_Estate_Assets_Parent_Box_Folder_Id__c,
Tax_Documents_Parent_Box_Folder_Id__c,
Medical_Records_Parent_Box_Folder_Id__c,
Funding_Parent_Box_Folder_Id__c,
Underwriting_Parent_Box_Folder_Id__c,
Registration_Parent_Box_Folder_Id__c,
Compliance_Parent_Box_Folder_Id__c,
Contact_Parent_Box_Folder_Id__c,
Performance_Reports_Parent_Box_Folder_Id__c,
Opportunity_Parent_Box_Folder_Id__c
from Account
where RecordTypeId = :householdAccountRTId
and Box_Folder_Id__c = null limit 1
];
new AccountBoxFolderCreationBatch ().execute(null,AccList);
System.debug('Callouts Used are:'+LIMITS.getCallouts());
Once we see the debug log, we can find the optimal batch size needed.
Src: Callout limits