If you create a sample meta field that is defined in the sample type, make sure that you specify the correct sampleTypeMetaID for it. In addition, the sampleDataType should be the same as defined in the sample type as defined in the sample type.
You can create a meta field that isn't defined by leaving the sampleTypeMetaID blank. This is not advisable though, and results in the meta field's value not to be searchable!
In case of a meta field with selectable value - data types CHECKBOX, COMBO and RADIO - make sure that you only specify the values that are listed in the sample type's optionValues property. In case of multiple selected values, separate each value with a comma.
This call will check if a meta field with the specified key already exists. If so it overwrites that meta field unless the value is the same; otherwise it creates a new meta field. Note: the sampleMetaID will be newly created on an overwrite.