The mobileapp::10001-ca-gmail is passed to us from the AUTOMATIC_PLACEMENTS_PERFORMANCE_REPORT in the Domain field.
<selector>
<fields>Domain</fields>
<fields>CampaignName</fields>
<fields>CampaignId</fields>
<fields>AdGroupName</fields>
<fields>AdGroupId</fields>
<fields>Impressions</fields>
<fields>Clicks</fields>
<fields>Cost</fields>
<fields>Conversions</fields>
<fields>ConversionValue</fields>
<predicates><field>CampaignStatus</field>
<operator>EQUALS</operator>
<values>ENABLED</values></predicates>
<predicates><field>AdGroupStatus</field>
<operator>EQUALS</operator>
<values>ENABLED</values></predicates>
<dateRange>
<min>20181024</min>
<max>20181024</max>
</dateRange>
</selector>
<reportName>AUTOMATIC_PLACEMENTS_PERFORMANCE_REPORT</reportName>
<reportType>AUTOMATIC_PLACEMENTS_PERFORMANCE_REPORT</reportType>
<dateRangeType>CUSTOM_DATE</dateRangeType>
<downloadFormat>XML</downloadFormat>
</reportDefinition>
Using the full domain "mobileapp::10001-ca-gmail" gives the same error from CampaignCriterionService when trying to create a negative placement.