Managing en administrate prepaid hours to cusomer in zoho desk

Good day,

As a Digital Agency, we have been looking for a solution for some time to administer and communicate pre-purchased hours in Zoho Desk. This is a solution where:

A pre-purchased number of hours can be added to a project or organization
The remaining balance of the purchased hours is visible to the customer in Zoho desk
An hourly proposal can be communicated
The customer must formally agree in the system to the proposed hours.
Upon completion and approval of the completed work by the customer, the hour proposal is automatically deducted from the Balance (purchased hour balance)

Does anyone have experience with connecting Zoho Desk with other systems where the described process is feasible?

I would like to hear from you and kind regards,

Raymond Hofman