How to make single API call with parallel logic

foreach (ResponseModel AccountSwap in invalidRecords) {
    this.ValidatePolicyExistParallel(AccountSwap, bpValidPolicyDataTable);
}

private void ValidatePolicyExistParallel(ResponseModel policyDetails, DataTable ValidDataTable) {
    Parallel.ForEach(invalidRecords, AccountSwap => {
        if (this.IsPolicyExistParallel(AccountSwap.CorrectPolicyNumber)) {
            var row = ValidDataTable.NewRow();
            row["IncorrectReference"] = policyDetails.IncorrectNumber;
            row["CorrectReference"] = policyDetails.CorrectNumber;
            ValidDataTable.Rows.Add(row);
        }
    });
}

private bool IsPolicyExistParallel(string policyNumber) {
    var accountId = GetId(policyNumber).Result;
    // This API will return BIGINT number as a response if the records exist
    return accountId != null;
}

foreach (ResponseModel AccountSwap in invalidRecords) {
    await this.ValidatePolicyExistAsync(AccountSwap, bpValidPolicyDataTable);
}

private async Task ValidatePolicyExistAsync(ResponseModel policyDetails, DataTable ValidDataTable) {
    if (await this.IsPolicyExistAsync(policyDetails.CorrectPolicyNumber)) {
        var row = ValidDataTable.NewRow();
        row["IncorrectReference"] = policyDetails.IncorrectNumber;
        row["CorrectReference"] = policyDetails.CorrectNumber;
        ValidDataTable.Rows.Add(row);
    }
}

private async Task IsPolicyExistAsync(string policyNumber) {
    var accountId = await GetIdAsync(policyNumber);
    // This API will return BIGINT number as a response if the records exist
    return accountId != null;
}

private async Task GetIdAsync(string policyNumber) {
    // Implement the asynchronous logic to call the "GetId" API
    // and return the result
}