I am writing a liquibase script for MS SQL and Oracle database.

    <changeSet author="root" id="CUSTOMER_SYNONYM" runOnChange="true">
        <preConditions onFail="MARK_RAN">
            <or>
                <dbms type="oracle"/>
                <dbms type="mssql"/>
            </or>
        </preConditions>
        <sql dbms="mssql">
            <![CDATA[
                IF NOT EXISTS (SELECT * FROM sys.synonyms WHERE name = 'CUSTOMER_SYNONYM')
                BEGIN
                EXEC('CREATE SYNONYM CUSTOMER_SYNONYM FOR PLT.CUSTOMER');
                END;
            ]]>
        </sql>
        <sql dbms="oracle">
            <![CDATA[
                DECLARE
                    synonym_exists NUMBER;
                BEGIN
                    SELECT COUNT(*)
                    INTO synonym_exists
                    FROM all_synonyms
                    WHERE synonym_name = 'CUSTOMER_SYNONYM' AND owner = 'PLT';

                    IF synonym_exists = 0 THEN
                        EXECUTE IMMEDIATE 'CREATE SYNONYM CUSTOMER_SYNONYM FOR PLT.CUSTOMER';
                    END IF;
                END;
            ]]>
        </sql>
    </changeSet>

I am getting the following error:

ORA-06550: line 2, column 26:
PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following:

   := . ( @ % ; not null range default character
 [Failed SQL: (6550) DECLARE
                                  synonym_exists NUMBER]

I tried running the same SQL in DBeaver and it worked.
I don’t understand what’s wrong here. Please correct me.