Deny API call with same payload parameter value like in the previous call (within a minute)

I guess we can make use of PopulateCache, LookupCache and Raise Fault.

First Use an Extract variable policy to get the proposalNumber.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ExtractVariables async="false" continueOnError="false" enabled="true" name="Extract-Variables-1">
    <DisplayName>Extract Variables-1</DisplayName>
    <Properties/>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
    <JSONPayload>
        <Variable name="number">
            <JSONPath>$.number</JSONPath>
        </Variable>
    </JSONPayload>
    <Source clearPayload="false">request</Source>
    <VariablePrefix>apigee</VariablePrefix>
</ExtractVariables>

Use a Lookup Cache to get the Value from Cache,

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<LookupCache async="false" continueOnError="false" enabled="true" name="Lookup-Cache-1">
    <DisplayName>Lookup Cache-1</DisplayName>
    <Properties/>
    <CacheKey>
        <Prefix/>
        <KeyFragment ref="apigee.number"/>
    </CacheKey>
    <Scope>Exclusive</Scope>
    <AssignTo>flowVar</AssignTo>
</LookupCache>

Use a PopulateCache to Cache the extracted prososalNumber(number in my example) with 60sec expiry time.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<PopulateCache async="false" continueOnError="false" enabled="true" name="Populate-Cache-1">
    <DisplayName>Populate Cache-1</DisplayName>
    <Properties/>
    <CacheKey>
        <Prefix/>
        <KeyFragment ref="apigee.number"/>
    </CacheKey>
    <Scope>Exclusive</Scope>
    <ExpirySettings>
        <TimeoutInSec>60</TimeoutInSec>
    </ExpirySettings>
    <Source>apigee.number</Source>
</PopulateCache>

Use a Raise Fault to raise an error based on some Conditions.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<RaiseFault async="false" continueOnError="false" enabled="true" name="Raise-Fault-1">
    <DisplayName>Raise Fault-1</DisplayName>
    <Properties/>
    <FaultResponse>
        <Set>
            <Headers/>
            <Payload contentType="text/plain"/>
            <StatusCode>500</StatusCode>
            <ReasonPhrase>Received Same Proposal Number in a Minute</ReasonPhrase>
        </Set>
    </FaultResponse>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</RaiseFault>

Conditions can be something like this,

	<Request>
            <Step>
                <Name>Extract-Variables-1</Name>
            </Step>
            <Step>
                <Name>Lookup-Cache-1</Name>
            </Step>
            <Step>
                <Name>Populate-Cache-1</Name>
                <Condition>flowVar != apigee.number</Condition>
            </Step>
            <Step>
                <Name>Raise-Fault-1</Name>
                <Condition>flowVar = apigee.number</Condition>
            </Step>
        </Request>

Use a payload like,

{"number":1}

When you make a call for the first time with a payload like {"number":1},

• the number will be extracted
• but the LookUpCache will not find any Cache for the extarctedNumber so the flow will continue and
• execute the PopulateCache to store the extarctedNumber in cache for 60seconds and
• the Raise Fault will be skipped.

When you make a call for the second time with same payload {"number":1} within a minute,

• the number will be extracted,
• LookupCache will get the cache and assign it to flowVar.
• as the flowVar(number) from LookupCache is equal to extractedNumber,
  • the Populate Cache will be skipped
  • RaiseFault will be executed

Note -

I have not tried these steps, so not sure if it is going to work. Try it on a sample proxy and check.

I have not followed/used naming conventions so take care of them in your proxy.