Hi Adam,

You can use the following endpoint to delete translation units with a filter:
example:
Method: Delete
url: /api/tmservice/tms/{tmId}/tus/{source}/{target}?startTuId=0&count=100
Body:
{
"fields": [
{
"name": "src",
"type": "SingleString",
"values":null
}
],
"expression": "\"src\" @ \"your source text\""
}

for Target text you can use "trg" instead of "src"

Operators for filtering: = , > , <, >= , <= , != , @ (contains) , !@ (does not contain), ~ (matches), !~ (does not match)

Suggestion :
You can test the filter expression before the delete using the filter translation units endpoint :
Method: Post
url: /api/tmservice/tms/{tmId}/tus/filter?source=en-gb&target=de-de&startTuId=0&count=100
Body:
{
"fields": [
{
"name": "src",
"type": "SingleString",
"values":null
}
],
"expression": "\"src\" @ \"your source text\""
}

Change the parameters according to your TM details.

If you need extra information for filtering let me know.

Thanks

/api/tmservice/tms/061117a7-4f93-41cd-a61c-0db3d75ebe94/tus/filter?source=de-de&target=af-za&startTuId=0&count=100

{
"fields": [
{
"name": "src",
"type": "SingleString",
"values":null
},
{
"name": "trg",
"type": "SingleString",
"values":null
}
],
"expression": "((\"src\"=\"string\") & (\"trg\"=\"string\"))"
}

resposne

{
"ErrorCode": "CoreError",
"Message": "Error: System - The data types ntext and varchar are incompatible in the equal to operator. (details: System.Data.SqlClient.SqlException (0x80131904): The data types ntext and varchar are incompatible in the equal to operator.\r\n at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)\r\n at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)\r\n at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)\r\n at System.Data.SqlClient.SqlDataReader.TrySetMetaData(_SqlMetaDataSet metaData, Boolean moreInfo)\r\n at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)\r\n at System.Data.SqlClient.SqlDataReader.TryConsumeMetaData()\r\n at System.Data.SqlClient.SqlDataReader.get_MetaData()\r\n at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption, Boolean shouldCacheForAlwaysEncrypted)\r\n at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)\r\n at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)\r\n at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)\r\n at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)\r\n at Sdl.LanguagePlatform.TranslationMemoryImpl.Storage.DbStorage.GetTUsWithAttributesAndContexts(DbCommand retrievalCmd, Boolean returnIdContext, Boolean returnContext, Dictionary`2 attributes, CultureInfo sourceCulture, CultureInfo targetCulture, Boolean cmIsPrecedingFollowing)\r\n at Sdl.LanguagePlatform.TranslationMemoryImpl.Storage.SqlStorage.GetTusFiltered(Int32 tmId, FilterExpression filter, Int32 startAfter, Int32 count, Boolean forward, Boolean idContextMatch, Boolean includeContextContent, TextContextMatchType textContextMatchType, CultureInfo sourceCulture, CultureInfo targetCulture)\r\n at Sdl.LanguagePlatform.TranslationMemoryImpl.TranslationUnitServerFilteringStrategy.Sdl.LanguagePlatform.TranslationMemoryImpl.ITranslationUnitFilteringStrategy.GetTusFiltered(PersistentObjectToken translationMemoryId, RegularIterator iter, FieldDefinitions fieldDefinitions, Boolean includeContextContent, TextContextMatchType textContextMatchType, CultureInfo sourceCulture, CultureInfo targetCulture, Boolean usesIdContextMatch)\r\n at Sdl.LanguagePlatform.TranslationMemoryImpl.ResourceManager.GetTranslationUnits(PersistentObjectToken tmId, RegularIterator iter, Boolean skipOptimize)\r\n at Sdl.LanguagePlatform.TranslationMemoryImpl.API.GetTranslationUnits(Container container, PersistentObjectToken tmId, RegularIterator& iter)\r\nClientConnectionId:08665320-4453-4efe-aadc-22d89a332995\r\nError Number:402,State:1,Class:16)"
}