Yes, API limits can be increased with the help of support team temporarily for an account.
For v1:
The number of API calls per hour is restricted to 1000. If your API request is received after the limit has been reached, freshservice will give you an error response. The "retry-after" value in the response header will tell you how long you need to wait before you send another API request.
For more details refer to our API v1 documentation: https://api.freshservice.com/
For v2:
Freshservice accounts created on or after 01-Sep-2020 will use minute-level rate limiting. The limits vary based on the freshservice plan. Certain API operations also have sub-limits within the overall limit. This limit is applied on an account-wide basis irrespective of factors such as the number of agents or IP addresses used to make the calls.

Accounts created before 01-Sep-2020 will eventually be migrated to minute-level rate limiting. The previous limits would continue to apply until the migration is completed.
For more details refer to our API v2 documentation: https://api.freshservice.com/v2/

Input for date fields is expected to be in one of the following formats:
YYYY-MM-DD
YYYY-MM-DDTHH:MM
YYYY-MM-DDTHH:MMZ
YYYY-MM-DDTHH:MM:SS
YYYY-MM-DDTHH:MM:SSZ
YYYY-MM-DDTHH:MM:SS±hh:mm
YYYY-MM-DDTHH:MM:SS±hh
YYYY-MM-DDTHH:MM:SS±hhmm
For more information, please click : https://api.freshservice.com/v2/#schema
If you have priority matrix enabled on your account, then the value passed in the API will be ignored and the priority matrix would set the priority for the ticket. If in case you do not want this, you can navigate to Admin > Priority Matrix and disable it.
A Webhook is a callback to an application or a web service that is triggered when a specific event occurs, this is configured using the workflow automator. This means you can set up a Webhook to look for a specific update, change or action to occur in your Service Desk and it will automatically push the information you specify to the application you want.
We are sorry it is not possible to associate a change to a ticket using API.
Yes, certain marketplace apps consume APIs, do reach out to our support team if you need further information on this.
If you are using API V1 then after the limit has been reached, freshservice will give you an error response. The "retry-after" value in the response header will tell you how long you need to wait before you send another API request.
To check the API limit using V2, You can check your current rate limit status by looking at the following HTTP headers which are returned in response to every API request.