ZAP will use a set of default values when importing APIs. In some cases these will not be suitable values for a specific application, and therefore will not exercise enough of the code. For example a username of “test” might not cause a new user to be created as it is not a valid email address.
For APIs defined using OpenAPI/Swagger you can specify the values you want ZAP to use via ZAP command line options.
For example the options:
-config formhandler.fields.field(0).fieldId=username \
-config formhandler.fields.field(0).value=test@example.com \
-config formhandler.fields.field(0).enabled=true \
-config formhandler.fields.field(1).fieldId=phone \
-config formhandler.fields.field(1).value=012345678 \
-config formhandler.fields.field(1).enabled=true
Will supply the following values to the named fields:
username -> test@example.com
phone -> 012345678
The above quote shows an command line example, but our ZAP microservice implementation depends on the ZAP Rest API. Maybe there is an Rest Endpoint for this configuration option?
rseedorff
commented
5 years ago 
As a user i would like to configure the OpenAPI scans with specific values instead of the default ones. More Informations on that can be found here: https://zaproxy.blogspot.com/2017/06/scanning-apis-with-zap.html
The above quote shows an command line example, but our ZAP microservice implementation depends on the ZAP Rest API. Maybe there is an Rest Endpoint for this configuration option?