How to configure MongoDB for REST?

Question

I wanted to configure MongoDB 6.x for rest. Now Ive read that you need to use directives. I tried to configure it with https://www.mongodb.com/docs/manual/reference/expansion-directives/#std-label-expansion-directives.

I have the following configuration:

# mongod.conf

# for documentation of all options, see:
#   http://docs.mongodb.org/manual/reference/configuration-options/

#start
# Where and how to store data.
storage:
  dbPath: /var/lib/mongodb
#  engine:
#  wiredTiger:

# where to write  logging data.
systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

# network interfaces
net:
  port: 28017
  bindIp: 127.0.0.1

# how the process runs
processManagement:
  timeZoneInfo: /usr/share/zoneinfo

#security:

#operationProfiling:

#replication:

#sharding:

## Enterprise-Only Options:

#auditLog:

#snmp:
__rest: "http://mongoconf.example.net:28017/test"
type: "string"
trim: "whitespace"
digest: "<string>"
digest_key: "<string>"`

Now I get the following error message: digest: "Not a valid, even length hex string"

Tried the configuration described "Expansion Directives Reference" at https://www.mongodb.com/docs/manual/reference/expansion-directives/#std-label-expansion-directives