freeswitch dialplan condition not working - freeswitch

Question

I am trying to understand db module.
Here is my dialplan for testing.
Here issue is that my condition is not working. Without condition its working fine.
Anyone please guide that how can i get this working ?
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<document type="freeswitch/xml">
<section name="dialplan" description="Test Dialplan">
<context name="default">
<extension name="919824012345">
<condition field="destination_number" expression="919824012345">
<action application="set" data="effective_destination_number=919824012345"/>
<action application="set" data="bridge_pre_execute_bleg_app=sched_hangup"/>
<action application="set" data="bridge_pre_execute_bleg_data=+6000 normal_clearing"/>
<action application="set" data="hangup_after_bridge=true"/>
<action application="set" data="continue_on_fail=TRUE"/>
<action application="set" data="call_processed=internal"/>
<action application="set" data="call_direction=outbound"/>
<action application="set" data="accountname=default"/>
<action application="set" data="origination_rates=ID:2|CODE:^91.*|DESTINATION:|CONNECTIONCOST:0.00000|INCLUDEDSECONDS:0|CT:|COST:0.20000|INC:60|INITIALBLOCK:1|RATEGROUP:1|MARKUP:0|CI:0|ACCID:24"/>
<action application="set" data="original_caller_id_name=919426223273"/>
<action application="set" data="original_caller_id_number=919824012345"/>
<action application="limit" data="db 24 user_24 1 !SWITCH_CONGESTION"/>
<condition field="${db(exists/realm/account_24)}" expression="^true$"/>
<condition field="${db(select/realm/account_24)}" expression="4"/>
<action application="set" data="var=${db(select/realm/account_24)}"/>
<action application="db" data="insert/realm/account_24/$${var}+1"/>
<anti-action application="hangup" data="${originate_disposition}"/>
</condition>
<anti-action application="db" data="insert/realm/account_24/1"/>
<action application="set" data="execute_on_anwer=transfer OUTBOUNDSERVICE XML default"/>
</condition>
<action application="bridge" data="[leg_timeout=30,absolute_codec_string=^^:PCMA:G729:PCMA]sofia/gateway/mygateway/919824012345"/>
</condition>
</extension>
</context>
</section>
</document>
I would like to achieve below
if exists account_24 then select the value of account_24 key.
If its value 4 or smaller then continue the call and add one more count.
If its value 4 then hangup call.
Once the call will be completed decrease its count up to 0.
In simple language, Count management to know how many calls are running for the customer. It should not more than assign to the customer.
Please, Let me know if required any more helps.