Hello!
It seems like there is no way to create a custom activity via API. It would be very useful for our app that we develop. For example, we want to add some custom activities to deals. But I have a little hope that I missed something 
Hi, @ogelal 
I can confirm this isn’t a feature. If you have a moment, adding your suggestion to the Ideas Community and getting some upvotes will be very helpful in getting your suggestion in front of the Product team. If you add a link back to your Idea post, I’ll be sure to give it an upvote to help get the ball rolling.
Best,
Jaycee
I am writing on behalf of our business to express our interest in a new feature that we believe would greatly benefit our operations within the HubSpot platform. Specifically, we would greatly appreciate the implementation of a Custom Activities and API for the same.
As a business, we have identified a crucial need for logging and tracking client visits to our establishment. It is essential for us to have a streamlined system that can accurately record when clients arrive and on what dates. While we currently utilize custom objects for this purpose, we have encountered limitations, such as the 500,000 record cap and the lack of efficiency in managing these objects.
By introducing a Custom Activities API, we believe we can overcome these challenges and significantly enhance our ability to track and log client visits. The API would allow us to create custom activities specifically designed for this purpose, providing us with a more efficient and scalable solution. It would enable us to seamlessly integrate the data into our existing workflows and leverage the full potential of the HubSpot platform.
The key benefits we foresee with the Custom Activities API include:
1. Improved Efficiency: By utilizing a dedicated API for custom activities, we can streamline the process of logging client visits, reducing manual effort and potential errors. This would save us valuable time and resources.
2. Scalability: With the current limit on custom objects, we anticipate that our data will soon exceed the threshold. The Custom Activities API would allow us to surpass this constraint and continue to record client visits without any disruptions.
3. Enhanced Reporting and Analysis: Having custom activities as a distinct entity would enable us to generate more accurate and meaningful reports, providing us with valuable insights into client behavior and visit patterns. This information would empower us to make data-driven decisions and optimize our business strategies.
We understand that implementing new features requires careful consideration and resources on your end. However, we strongly believe that the Custom Activities API would not only benefit our business but also be a valuable addition for many other HubSpot users facing similar challenges.
We kindly request that you take our suggestion into serious consideration and assess the feasibility of introducing the Custom Activities API. We are confident that its implementation would enhance the versatility and flexibility of the HubSpot platform, catering to the diverse needs of businesses across various industries.
Thank you for your attention to this matter. We look forward to any updates or feedback regarding the possibility of integrating the Custom Activities API into HubSpot. Your support would be greatly appreciated, and we are excited about the potential this feature holds for improving our operations.