Unable to set the CreditAmount in JournalLineItem for journals created with Business Rule

It might be better to use DecimalAndNoData objects to assign JournalLineItem.DebitAmount and JournalLineItem.CreditAmount.  I don't think you can directly assign a decimal value to these.

            .DebitAmount = New DecimalAndNoData(0.0D, True),
            .CreditAmount = New DecimalAndNoData(-150, False)

Putting it all together:

Sub CreateJournal(ByVal sessionInfo As SessionInfo)
    Try
        ' member IDs
        Dim entityId As Integer = BRApi.Finance.Members.GetMemberId(sessionInfo, DimType.Entity.Id, "100_US")
        Dim debitAccountId As Integer = BRApi.Finance.Members.GetMemberId(sessionInfo, DimType.Account.Id, "10220030")
        Dim creditAccountId As Integer = BRApi.Finance.Members.GetMemberId(sessionInfo, DimType.Account.Id, "10220050")
        Dim flowId As Integer = BRApi.Finance.Members.GetMemberId(sessionInfo, DimType.Flow.Id, "EndBal")
        Dim intercompanyId As Integer = BRApi.Finance.Members.GetMemberId(sessionInfo, DimType.IC.Id, "None")

        '  journal header
        Dim journalHeader As New JournalHeader() With {
            .Name = "Test_Journal",
            .Description = "This is a test journal",
            .WorkflowProfileID = sessionInfo.WorkflowClusterPk.ProfileKey,
            .JournalStatus = JournalStatus.Working,
            .IsSingleEntity = False,
            .MemberIds = New KeyedByDimTypeList(Of Integer)() With {
                .Scenario = sessionInfo.WorkflowClusterPk.ScenarioKey,
                .Time = sessionInfo.WorkflowClusterPk.TimeKey
            }
        }

        ' line items
        Dim debitLineItem As New JournalLineItem() With {
            .EntityId = entityId,
            .AccountId = debitAccountId,
            .FlowId = flowId,
            .ICId = intercompanyId,
            .DebitAmount = New DecimalAndNoData(150, False),
            .CreditAmount = New DecimalAndNoData(0.0D, True)
        }

        Dim creditLineItem As New JournalLineItem() With {
            .EntityId = entityId,
            .AccountId = creditAccountId,
            .FlowId = flowId,
            .ICId = intercompanyId,
            .DebitAmount = New DecimalAndNoData(0.0D, True),
            .CreditAmount = New DecimalAndNoData(-150, False)
        }

        ' line items list
        Dim journalLineItems As New List(Of JournalLineItem) From {
            debitLineItem,
            creditLineItem
        }

        ' Create and save the journal
        Dim journal As New Journal(journalHeader, journalLineItems)
        BRApi.Journals.Metadata.SaveJournalOrTemplateUsingIds(sessionInfo, journal, False, True)

    Catch ex As Exception
        Throw ErrorHandler.LogWrite(sessionInfo, New XFException(sessionInfo, ex))
    End Try
End Sub

Curious why you are making the credit amount negative?...