Kafka Connect FileConfigProvdier not working - db2

Question

I'm running Kafka Connect with JDBC Source Connector for DB2 in standalone mode. Everything works fine, but I'm putting the passwords and other sensitive info into my connector file in plain text. I'd like to remove this, so I found that FileConfigProvider can be used:
https://docs.confluent.io/current/connect/security.html#fileconfigprovider
However, when I try to use this it does not seem to pick up my properties file. Here's what I'm doing:
connect.standalone.oroperties -
config.providers=file
config.providers.file.class=org.apache.kafka.common.config.provider.FileConfigProvider
secrets.properties -
password=thePassword
Source Config -
"connection.password": "${file:/Users/me/app/context/src/main/kafkaconnect/connector/secrets.properties:password}",
"table.whitelist": "MY_TABLE",
"mode": "timestamp",
When I try to load my source connector (via rest api) I get the following error:
{"error_code":400,"message":"Connector configuration is invalid and contains the following 2 error(s):\nInvalid value com.ibm.db2.jcc.am.SqlInvalidAuthorizationSpecException: [jcc][t4][2013][11249][4.26.14] Connection authorization failure occurred. Reason: User ID or Password invalid. ERRORCODE=-4214, SQLSTATE=28000 for configuration Couldn't open connection to jdbc:db2://11.1.111.111:50000/mydb\nInvalid value com.ibm.db2.jcc.am.SqlInvalidAuthorizationSpecException: [jcc][t4][2013][11249][4.26.14] Connection authorization failure occurred. Reason: User ID or Password invalid. ERRORCODE=-4214, SQLSTATE=28000 for configuration Couldn't open connection to jdbc:db2://11.1.111.111:50000/mydb\nYou can also find the above list of errors at the endpoint /{connectorType}/config/validate"}
The password I'm providing is correct. It works if I just hardcode it into my source json. Any ideas? Thanks!
Edit: As a note, I get similar results on the sink side inserting into a Postgres database.
Edit: Result of GET /connectors:
{
"name": "jdbc_source_test-dev",
"config": {
"connector.class": "io.confluent.connect.jdbc.JdbcSourceConnector",
"timestamp.column.name": "UPDATED_TS",
"connection.password": "${file:/opt/connect-secrets.properties:dev-password}",
"validate.non.null": "false",
"table.whitelist": "MY_TABLE",
"mode": "timestamp",
"topic.prefix": "db2-test-",
"transforms.extractInt.field": "kafka_id",
"_comment": "The Kafka topic will be made up of this prefix, plus the table name ",
"connection.user": "username",
"name": "jdbc_source_test-dev",
"value.converter": "org.apache.kafka.connect.json.JsonConverter",
"connection.url": "jdbc:db2://11.1.111.111:50000/mydb",
"key.converter": "org.apache.kafka.connect.storage.StringConverter"
},
"tasks": [
{
"connector": "jdbc_source_test-dev",
"task": 0
}
],
"type": "source"
}