Hi Anita,
We corresponded via email, but I will answer here as well. You cannot add Adobe Stock to a JWT service account unless you are a Stock for Enterprise customer. Since you have a subscription plan, that is not enterprise and therefore not eligible.
Some other products, such as PDF Services, offer JWT accounts, but those cannot be used with the Stock API. Instead, you may use the OAuth integration type, and have your users sign in with their personal login. This type of integration cannot be automated, however.
Here are more resources. If you are interested in become an Enterprise customer, please contact the team in the first link.
- Adobe Stock for Enterprise program information
- Stock API business FAQ