'longtext' datatype in xsd.

I am creating CDT for one table stored in cloud database but one column with datatype 'longtext' is not fetched in the CDT. So I have tried to add this column explicitly in the downloaded XSD file of this CDT by using the below code:

<xsd:element name="abc" nillable="true" type="xsd:string">
<xsd:annotation>
<xsd:appinfo source="appian.jpa">@Column(name="ABC", columnDefinition="LONGTEXT")</xsd:appinfo>
</xsd:annotation>
</xsd:element>

It is saved properly. Then I have created one constant using this CDT. and used it as 'Data Store Entity' field in 'Export DataStore Entity to Excel' smart service but it is not working and the node is failed with the below error message:

Please help me why the error is there.

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