GoogleアカウントじゃないメアドをGCPのIAMに登録しようとしたらエラーになる

はじめに

Terraformでgoogleアカウント以外のアカウントをIAMに登録しようとしたら、すごく分かりづらいエラーになってハマったため、メモしておく

terraformでのエラー内容

terraform plan時はエラーにならなくて、terraform apply時に以下のエラーが出る。

Error: Error applying plan:

1 error(s) occurred:

* google_project_iam_policy.projects: 1 error(s) occurred:

* google_project_iam_policy.projects: Error setting project IAM policy: Error applying IAM policy for project "project-name". \
Policy is &cloudresourcemanager.Policy{AuditConfigs:[]*cloudresourcemanager.AuditConfig(nil), \
Bindings:[]*cloudresourcemanager.Binding{(*cloudresourcemanager.Binding)(0xc00026aba0), \
 (*cloudresourcemanager.Binding)(0xc00026ac60), (*cloudresourcemanager.Binding)(0xc00026acc0),\
 (*cloudresourcemanager.Binding)(0xc00026ad20), (*cloudresourcemanager.Binding)(0xc00026ad80), \
 (*cloudresourcemanager.Binding)(0xc00026ae40), (*cloudresourcemanager.Binding)(0xc00026af00),\
 (*cloudresourcemanager.Binding)(0xc00026b140), (*cloudresourcemanager.Binding)(0xc00026b1a0),\
 (*cloudresourcemanager.Binding)(0xc00026b200), (*cloudresourcemanager.Binding)(0xc00026b2c0),\
 (*cloudresourcemanager.Binding)(0xc00026b380), (*cloudresourcemanager.Binding)(0xc00026b440),\
 (*cloudresourcemanager.Binding)(0xc00026b680), (*cloudresourcemanager.Binding)(0xc00026b6e0),\
 (*cloudresourcemanager.Binding)(0xc00026b740), (*cloudresourcemanager.Binding)(0xc00026b800),\
 (*cloudresourcemanager.Binding)(0xc00026b8c0), (*cloudresourcemanager.Binding)(0xc00026b920),\
 (*cloudresourcemanager.Binding)(0xc00026b980)}, Etag:"", Version:0,\
 ServerResponse:googleapi.ServerResponse{HTTPStatusCode:0, Header:http.Header(nil)}, \
ForceSendFields:[]string(nil), NullFields:[]string(nil)}, error is googleapi: Error 400: \
User [e-mail] does not exist., badRequest

developer consoleで確認

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