When using slapadd to add an entry, it shows error "The first database does not allow slapadd; using the first available one (2)".

Issue

When using slapadd to add an entry, it shows error "The first database does not allow slapadd; using the first available one (2)".
The customer use command as below:

slapadd -l text.ldif
The first database does not allow slapadd; using the first available one (2)
-#################### 100.00% eta   none elapsed                 spd   9.6 k/s
Closing DB...

But if the customer remove the monitor database lines in slapd.conf, it shows no error.