You are getting this warning because ONTAP 8.1.2 was released after ZExplore (ZEDI) was updated. In other words, ONTAP 8.1.2 api documentation is not included in ZEDI.
In most cases, you can ignore this warning because ZEDI automatically loads the ONTAPI version with the closest match. e.g. since ZEDI did not find Ontapi 1.19 7-Mode, it must have automatically loaded Ontapi 1.15 7-Mode.
Unless you are looking for some APIs which are newly added in ONTAP 8.1.2 or using some APIs which have undergone some change in ONTAP 8.1.2, you will be just fine using Ontapi 1.15 7-Mode by virtue of the backward-compatibility of ONTAP APIs.
This or a compatible version of ontapi is planned/expected to be included in upcoming release of NMSDK containing the updated ZEDI.
To check the ontapi version on the filer/storage system, use "system-get-ontapi-version" api (under "system" category).