Error on Syntax for rule with custom field

[Vasco]

Hi!
I'm trying to create a automation rule for a certain type of issues based on the time.

This should be a Scheduled task.

When I tested with

{{cf[10100].dayOfMonth}} = {{now.dayOfMonth}}

or with:

issuetype = 'Offboarding'

it run as expected, but when doing an intersection with the JQL:

issuetype = 'Offboarding' AND {{cf[10100].dayOfMonth}} = {{now.dayOfMonth}} 

I got the below error:

Error running query for scheduled JQL trigger: "(issuetype = 'Offboarding' AND = 21) AND (project in (10008))" - Error in the JQL Query: Expecting a field name but got '='. You must surround '=' in quotation marks to use it as a field name. (line 1, character 33)

doing

issuetype = 'Offboarding' and cf[10100] < now()

will work but not for the day at 00:00H

I did some try error but went nowhere. Can you help me understanding this?
Best Regards
Vasco