Please you help trying to understand what is wrong with my configuration as it looks like I complying with documentation published here:
<?xml version="1.0" encoding="UTF-8"?>
<soap:Header>
<requestId>8b3d2714fcb76850795ffb403522a7d7</requestId>
<responseTime>441</responseTime>
</ResponseHeader>
</soap:Header>
<soap:Body>
<soap:Fault>
<faultcode>soap:Server</faultcode>
<faultstring>[ProposalLineItemProgrammaticError.INVALID_SIZES @
[0].creativePlaceholders;
trigger:'[Size=1x1-null|TemplateId=null|CreativeSizeType=INTERSTITIAL]']</faultstring>
<detail>
<message>[ProposalLineItemProgrammaticError.INVALID_SIZES @
[0].creativePlaceholders;
trigger:'[Size=1x1-null|TemplateId=null|CreativeSizeType=INTERSTITIAL]']</message>
<errors xsi:type="ProposalLineItemProgrammaticError"
<fieldPath>[0].creativePlaceholders</fieldPath>
<fieldPathElements>
<index>0</index>
</fieldPathElements>
<fieldPathElements>
<field>creativePlaceholders</field>
</fieldPathElements>
<trigger>[Size=1x1-null|TemplateId=null|CreativeSizeType=INTERSTITIAL]</trigger>
<errorString>ProposalLineItemProgrammaticError.INVALID_SIZES</errorString>
<reason>UNKNOWN</reason>
</errors>
</ApiExceptionFault>
</detail>
</soap:Fault>
</soap:Body>
</soap:Envelope>