watch for new files on FTP Folder

we are try to using the following config to trigger a build, if some file is placed in one of the two `FOLDER_*` directories.

But nothing happens, any idea whats wrong?

```
properties([
disableConcurrentBuilds(),
buildDiscarder(logRotator(numToKeepStr: '30')),
pipelineTriggers([
URLTrigger(
cronTabSpec: 'H/5 09-18 * * 1-5',
entries: [
URLTriggerEntry(
url: "ftp://${ftpUrl}/FOLDER_1/",
username: ftpUser,
password: ftpPw,
contentTypes: [
MD5Sum()
]
),
URLTriggerEntry(
url: "ftp://${ftpUrl}/FOLDER_2/",
username: ftpUser,
password: ftpPw,
contentTypes: [
MD5Sum()
]
)
]
)
])
])
```

the logs are here:

```
[URLTrigger] - Poll with a URL

Inspecting Monitor a change of the content content for URL ftp://${ftpUrl}/FOLDER_1

Polling started on Mar 30, 2020 5:21:00 PM
Polling for the job XYZ
Looking nodes where the poll can be run.
Looking for a candidate node to run the poll.
Trying to find an eligible node with the assigned project label master.

Polling on master.
Resolving environment variables using global values

Polling complete. Took 0.28 sec.
No changes.

```