SigParser is configured by default to a low number of daily API requests so your other Salesforce applications don't get starved of requests. SigParser can sometimes use a lot of API requests when doing large sync jobs.
Most organizations have 15,000 + (1,000 x # of users) allowed per day. Unlimited or Performance editions get 15,000 + (5,000 x # of users). If limit is hit the remaining work will be done the next day. You can purchase more requests per day from Salesforce.
The more Salesforce users you have the more API requests your organization will have.
To increase your API request limit do the following:
Login to SigParser
Go to More -> Connectors
Click the Salesforce connector name
Click Configure Sync
Click Show Advanced Settings
Increase the API request limit to a higher value.