Generating Historical Metrics in Google Ads

According to the documentation To generate historical metrics: Create a KeywordPlan, KeywordPlanCampaigns, KeywordPlanAdGroups, KeywordPlanCampaignKeywords, and KeywordPlanAdGroupKeywords. Call KeywordPlanService.GenerateHistoricalMetrics with that keyword plan.

These plans come out as a 4-element, slash-delimited string, e.g. customers/1879809528/keywordPlanCampaigns/413340892. However, after modifying the sample code to call GenerateHistoricalMetrics I find that the API at that point expects a long, the KeywordPlanId.

Is this number the 4th item in the plan string? Apparently not, as this slice out of the trace logs indicates:

... Response -------- Headers: {   "content-disposition": "attachment",   "request-id": "ahE6lqAnzToj3H65rHtHbA",   "date": "Mon, 30 May 2022 06:39:19 GMT",   "alt-svc": "h3=\":443\"; ma=2592000,h3-29=\":443\"; ma=2592000,h3-Q050=\":443\"; ma=2592000,h3-Q046=\":443\"; ma=2592000,h3-Q043=\":443\"; ma=2592000,quic=\":443\"; ma=2592000; v=\"46,43\"" } { "results": [ { "resourceName": "customers/1879809528/keywordPlanCampaigns/413340892" } ] } ... Response -------- ... Fault: {   "StatusCode": 3,   "Details": "Request contains an invalid argument.",   "RequestId": "mMZTztmu4ufHpgJ77xph9Q",   "Failure": {     "errors": [       {         "errorCode": {           "keywordPlanError": "KEYWORD_PLAN_NOT_FOUND"         },         "message": "No plan with planId[413340892] exists"       }     ],     "requestId": "mMZTztmu4ufHpgJ77xph9Q"   } } 

So how does one get from plan to metrics?